Engine & Driveability Problems: 7 Engine Won't Crank or Start

Engine Won't Crank or Start

What To Do When Your Car Won't Start

Every engine requires four basic ingredients to start: sufficient cranking speed, good compression, adequate ignition voltage (with correct timing) and fuel (a relatively rich air/fuel mixture initially). So if your car fails to start, you can assume it lacks one of these four essential ingredients. But which one?

To find you, you need to analyze the situation. If the engine won't crank, you are probably dealing with a starter or battery problem. Has the starter been acting up? (unusual noises, slow cranking, etc.). Is this the first time the engine has failed to crank or start, or has it happened before? Have the starter, battery or battery cables been replaced recently? Might be a defective part. Has the battery been running down? Might be a charging problem. Have there been any other electrical problems? The answers to these questions should shed some light on what might be causing the problem.

If an engine cranks but refuses to start, it lacks ignition, fuel or compression. Was it running fine but quit suddenly? The most likely causes here would be a failed fuel pump, ignition module or broken overhead cam timing belt. Has the engine been getting progressively harder to start? If yes, consider the engine's maintenance and repair history.

NO START DIAGNOSIS

What happens when you attempt to start the engine? If nothing happens when you turn the key, check the battery to determine its state of charge. Many starters won't do a thing unless there is at least 10 volts available from the battery. A low battery does not necessarily mean the battery is the problem, though. The battery may have been run down by prolonged cranking while trying to start the engine. Or, the battery's low state of charge may be the result of a charging system problem. Either way, the battery needs to be recharged and tested.

If the battery is low, the next logical step might be to try starting the engine with another battery or a charger. If the engine cranks normally and roars to life, you can assume the problem was a dead battery, or a charging problem that allowed the battery to run down. If the battery accepts a charge and tests okay, checking the output of the charging system should help you identify any problems there.

A charging system that is working properly should produce a charging voltage of somewhere around 14 volts at idle with the lights and accessories off. When the engine is first started, the charging voltage should rise quickly to about two volts above base battery voltage, then taper off, leveling out at the specified voltage. The exact charging voltage will vary according to the battery's state of charge, the load on the electrical system, and temperature. The lower the temperature, the higher the charging voltage. The higher the temperature, the lower the charging voltage. The charging range for a typical alternator might be 13.9 to 14.4 volts at 80 degrees F, but increase to 14.9 to 15.8 volts at subzero temperatures.

If the charging system is not putting out the required voltage, is it the alternator or the regulator? Full fielding the alternator to bypass the regulator should tell you if it is working correctly. Or, take the alternator to a parts store and have it bench tested. If the charging voltage goes up when the regulator is bypassed, the problem is the regulator (or the engine computer in the case of computer-regulated systems). If there is no change in output voltage, the alternator is the culprit.

Many times one or more diodes in the alternator rectifier assembly will have failed, causing a drop in the unit's output. The alternator will still produce current, but not enough to keep the battery fully charged. This type of failure will show up on an oscilloscope as one or more missing humps in the alternator waveform. Most charging system analyzers can detect this type of problem.

ENGINE CRANKING PROBLEMS

If your car won't start because the engine won't crank or cranks slowly (and the battery is fully charged), you can focus your attention on the starter circuit. A quick way to diagnose cranking problems is to switch on the headlights and watch what happens when you attempt to start the engine. If the headlights go out, a poor battery cable connection may be strangling the flow of amps. All battery cable connections should be checked and cleaned along with the engine-to-chassis ground straps.

Measuring the voltage drop across connections is a good way to find excessive resistance. A voltmeter check of the cable connections should show no more than 0.1 volt drop at any point, and no more than 0.4 volts for the entire starter circuit. A higher voltage drop would indicate excessive resistance and a need for cleaning or tightening.

Slow cranking can also be caused by undersized battery cables. Some cheap replacement cables have small gauge wire encased in thick insulation. The cables look the same size as the originals on the outside, but inside there is not enough wire to handle the amps.

If the headlights continue to shine brightly when you attempt to start the engine and nothing happens (no cranking), voltage is not reaching the starter. The problem here is likely an open or misadjusted park/neutral safety switch, a bad ignition switch, or a faulty starter relay or solenoid. Fuses and fusible links should also be checked because overloads caused by continuous cranking or jump starting may have blown one of these protective devices.

If the starter or solenoid clicks but nothing else happens when you attempt to start the engine, there may not be enough amps to spin the starter. Or the starter may be bad. A poor battery cable, solenoid or ground connection, or high resistance in the solenoid itself may be the problem. A voltage check at the solenoid will reveal if battery voltage is passing through the ignition switch circuit. If the solenoid or relay is receiving battery voltage but is not closing or passing enough amps from the battery to spin the starter motor, the solenoid ground may be bad or the contacts in the solenoid may be worn, pitted or corroded. If the starter cranks when the solenoid is bypassed, a new solenoid is needed, not a starter.

Most engines need a cranking speed of 200 to 300 rpm for your car to start, so if the starter is weak and can't crank the engine fast enough to build compression, the engine won't start. In some instances, a weak starter may crank the engine fast enough but prevent it from starting because it draws all the power from the battery and does not leave enough for the injectors or ignition system.

If the lights dim and there is little or no cranking when you attempt to start the engine, the starter may be locked up, dragging or suffering from high internal resistance, worn brushes, shorts or opens in the windings or armature. A starter current draw test will tell you if the starter is pulling too many amps.

A good starter will normally draw 60 to 150 amps with no load on it, and up to 200 amps or more while cranking the engine. The no-load amp draw depends on the rating of the starter while the cranking amp draw depends on the displacement and compression of the engine. Always refer to the OEM specs for the exact amp values. Some "high torque" GM starters, for example, may have a no load draw of up to 250 amps. Toyota starters on four-cylinder engines typically draw 130 to 150 amps, and up to 175 amps on six-cylinder engines.

An unusually high current draw and low free turning speed or cranking speed typically indicates a shorted armature, grounded armature or field coils, or excessive friction within the starter itself (dirty, worn or binding bearings or bushings, a bent armature shaft or contact between the armature and field coils). The magnets in permanent magnet starters can sometimes break or separate from the housing and drag against the armature.

A starter that does not turn at all and draws a high current may have a ground in the terminal or field coils, or a frozen armature. On the other hand, the start may be fine but can't crank the engine because the engine is seized or hydrolocked. So before you condemn the starter, try turning the engine over by hand. Won't budge? Then the engine is probably locked up.

A starter that won't spin at all and draws zero amps has an open field circuit, open armature coils, defective brushes or a defective solenoid. Low free turning speed combined with a low current draw indicates high internal resistance (bad connections, bad brushes, open field coils or armature windings).

If the starter motor spins but fails to engage the flywheel, the cause may be a weak solenoid, defective starter drive or broken teeth on the flywheel. A starter drive that is on the verge of failure may engage briefly but then slip. Pull the starter and inspect the drive. It should turn freely in one direction but not in the other. A bad drive will turn freely in both directions or not at all.

ENGINE CRANKS BUT YOUR CAR WILL NOT START

When the engine cranks normally but you car won't start, you need to check ignition, fuel and compression. Ignition is easy enough to check with a spark tester or by positioning a plug wire near a good ground. No spark? The most likely causes would be a failed ignition module, distributor pickup or cranksahaft position (CKP) sensor.

A tool such as an Ignition System Simulator can speed the diagnosis by quickly telling you if the ignition module and coil are capable of producing a spark with a simulated timing input signal. If the simulated signal generates a spark, the problem is a bad distributor pickup or crankshaft position sensor. No spark would point to a bad module or coil. Measuring ignition coil primary and secondary resistance can rule out that component as the culprit.

Module problems as well as pickup problems are often caused by loose, broken or corroded wiring terminals and connectors. Older GM HEI ignition modules are notorious for this. If you are working on a distributor less ignition system with a Hall effect crankshaft position sensor, check the sensor's reference voltage (VRef) and ground. The sensor must have 5 volts or it will remain permanently off and not generate a crank signal (which should set a fault code). Measure VRef between the sensor power supply wire and ground (use the engine block for a ground, not the sensor ground circuit wire). Don't see 5 volts? Then check the sensor wiring harness for loose or corroded connectors. A poor ground connection will have the same effect on the sensor operation as a bad VRef supply. Measure the voltage drop between the sensor ground wire and the engine block. More than a 0.1 voltage drop indicates a bad ground connection. Check the sensor mounting and wiring harness.

If a Hall effect crank sensor has power and ground, the next thing to check would be its output. With nothing in the sensor window, the sensor should be "on" and read 5 volts (VRef). Measure the sensor D.C. output voltage between the sensor signal output wire and ground (use the engine block again, not the ground wire). When the engine is cranked, the sensor output should drop to zero every time the shutter blade, notch, magnetic button or gear tooth passes through the sensor. No change in voltage would indicate a bad sensor that needs to be replaced.

If the primary side of the ignition system seems to be producing a trigger signal for the coil but the voltage is not reaching the plugs, a visual inspection of the coil tower, distributor cap, rotor and plug wires should be made to identify any defects that might be preventing the spark from reaching its intended destination.

ENGINE CRANKS, HAS SPARK BUT WILL NOT START

If you see a good hot spark when you crank the engine, but it won't start, check for fuel. The problem might be a bad fuel pump.

On an older engine with a carburetor, pump the throttle linkage and look for fuel squirting into the carburetor throat. No fuel? Possible causes include a bad mechanical fuel pump, stuck needle valve in the carburetor, a plugged fuel line or fuel filter.

On newer vehicles with electronic fuel injection, connect a pressure gauge to the fuel rail to see if there is any pressure in the line. No pressure when the key is on? Check for a failed fuel pump, pump relay, fuse or wiring problem. On Fords, don't forget to check the inertia safety switch which is usually hidden in the trunk or under a rear kick panel. The switch shuts off the fuel pump in an accident. So if the switch has been tripped, resetting it should restore the flow of fuel to the engine. Lack of fuel can also be caused by obstructions in the fuel line or pickup sock inside the tank. And don't forget to check the fuel gauge. It is amazing how many no starts are caused by an empty fuel tank.

There is also the possibility that the fuel in the tank may be heavily contaminated with water or overloaded with alcohol. If the tank was just filled, bad gas might be causing the problem.

On EFI-equipped engines, fuel pressure in the line does not necessarily mean the fuel is being injected into the engine. Listen for clicking or buzzing that would indicate the injectors are working. No noise? Check for voltage and ground at the injectors. A defective ECM may not be driving the injectors, or the EFI power supply relay may have called it quits. Some EFI-systems rely on input from the camshaft position sensor to generate the injector pulses. Loss of this signal could prevent the system from functioning.

Even if there is fuel and it is being delivered to the engine, a massive vacuum leak could be preventing the engine from starting. A large enough vacuum leak will lean out the air/fuel ratio to such an extent that the mixture won't ignite. An EGR valve that is stuck wide open, a disconnected PCV hose, loose vacuum hose for the power brake booster, or similar leak could be the culprit. Check all vacuum connections and listen for unusual sucking noises while cranking.

ENGINE HAS FUEL AND SPARK BUT WILL NOT START

An engine that has fuel and spark, no serious vacuum leaks and cranks normally should start. The problem is compression. If it is an overhead cam engine with a rubber timing belt, a broken timing belt would be the most likely cause especially if the engine has a lot of miles on it. Most OEMs recommend replacing the OHC timing belt every 60,000 miles for preventative maintenance, but many belts are never changed. Eventually they break, and when they do the engine stops dead in its tracks. And in engines that lack sufficient valve-to-piston clearance as many import engines and some domestic engines do, it also causes extensive damage (bent valves and valvetrain components & sometimes cracked pistons).

Overhead cams can also bind and break if the head warps due to severe overheating, or the cam bearings are starved for lubrication. A cam seizure may occur during a subzero cold start if the oil in the crankcase is too thick and is slow to reach the cam (a good reason for using 5W-20 or 5W-30 for winter driving). High rpm cam failure can occur if the oil level is low or the oil is long overdue for a change.

With high mileage pushrod engines, the timing chain may have broken or slipped. Either type of problem can be diagnosed by doing a compression check and/or removing a valve cover and watching for valve movement when the engine is cranked.

A blown head gasket may prevent an engine from starting if the engine is a four cylinder with two dead cylinders. But most six or eight cylinder engines will sputter to life and run roughly even with a blown gasket. The gasket can, however, allow coolant to leak into the cylinder and hydrolock the engine.

Engine & Driveability Problems: 6 Car Won't Start?

Car Won't Start?

YOU TRY TO START YOUR CAR BUT IT WON'T START

What should you do when your car won't start? Diagnosing a no-start condition requires a logical approach to figuring out what might be preventing your car from starting. Below is a list of possible causes that can prevent your car from starting.

When you turn the ignition key to start your car, or press the START button, voltage from the battery flows through the ignition switch to the Park/Neutral safety switch and/or brake pedal or clutch pedal safety switch (you have to push the pedal down before the circuit will complete) to the starter relay or solenoid. When the relay or solenoid is energized by voltage from the ignition switch circuit, it closes a contact that routes more power from the battery directly to the starter to crank the engine. The starter motor spins, pushes the starter drive gear to engage the flywheel and cranks the engine.

If the engine fails to crank, there is a fault in one of the components in the battery/ignition/starter circuit.

COMMON CAUSES OF NO-CRANK NO-START

Low battery (Check battery voltage, recharge if low, or jump start with another vehicle or battery charger).

Loose or corroded battery cables (Inspect, clean and tighten BOTH ends of BOTH battery cables).

Bad starter relay wiring connections or ground connection (Inspect, clean, tighten wiring connections).

Bad starter relay/solenoid (Check for voltage at the relay, if relay has voltage but there is no "click" when key is turned to start, replace relay).

Bad starter (Jump battery voltage direct to starter to see if it spins, or remove starter and have it bench tested at auto parts store).

Damaged starter drive or teeth on flywheel (Remove starter and inspect drive gear and flywheel teeth, replace damaged parts if necessary).

Bad ignition switch (Check to see if voltage reaches starter relay/solenoid when turn to start. If not, check for open P/N switch and brake or clutch pedal switch. Replace ignition if defective).

Open P/N safety switch, or open Brake Pedal Safety Switch (automatic transmission) or open Clutch Pedal Switch (manual transmission). Bypass switch with jumper wire to see if engine cranks, or use test light or voltmeter to check for voltage passing through switch when ignition is turned to start.

Dead Smart Key Fob battery Refer to owners manual for emergency starting procedure if your Key fob won't start your car. On some vehicles, placing the fob next to the push start button, pressing the Start button with the fob, or inserting the fob into a special slot on the instrument panel, steering column or center console may allow it to communicate with the ignition system so your engine will crank and start.

Engine seized due to bearing failure or internal damage (Use a socket and long handle to see if the engine can be turned by hand, if not the engine is locked up).

Engine hydrolocked due to coolant leak from leaky head gasket (Use socket and wrench to see if engine rotates, remove spark plugs and see if coolant comes out or engine can not be cranked with plugs out).

ENGINE CRANKS OKAY BUT WON'T START

If the engine cranks over normally when you attempt to start your car, but the engine does not start, the problem may be NO FUEL, NO SPARK or NO COMPRESSION. The engine needs adequate fuel pressure, a properly timed spark and normal compression to start.

TIP: To find why the engine won't start, remove the air inlet tube from the throttle body, push the throttle open and spray a small amount of aerosol starting fluid into the engine. Crank the engine. IF it has spark and compression but NO FUEL, it will start and run a few seconds before dying. If it does NOT start, it probably has NO SPARK.

TIP: Another method to check for spark is to pull a spark plug wire off of a spark plug (if it has plug wires, coil-on-plug ignitions do not) and place the open end of the plug wire near a metal surface on the engine. Have a helper crank the engine while you watch for a spark. DO NOT hold the wire while doing this as it can shock you. If you see a spark, the problem is not spark, but most likely NO FUEL or NO COMPRESSION. If you do not see a spark, the problem is in the IGNITION CIRCUIT.

TIP: Proper fuel pressure is critical for fuel injected engines to start and run. You should hear the fuel pump inside the fuel tank buzz for a couple of seconds when the ignition is turned on (no buzz means the pump is not running and the engine is not getting fuel). You can smell the tailpipe for gasoline vapors after cranking the engine. If you smell gas, the problem is likely not fuel but NO SPARK. You can also remove the plastic cap and press the schraeder valve test fitting on the fuel rail to see if there is any fuel pressure to the engine (not a very accurate test because fuel pressure must be at a certain level for the engine to start, for that you need a gauge). Even so, no fuel at the fuel rail would tell you fuel is not getting to the engine.

FUEL RELATED CAUSES OF "NO START"

Anti-Theft system issue. If your Anti-Theft light is flashing, the anti-theft system is disabling the fuel pump to prevent the engine from starting. The problem could be a defective chip in a smart key, or a dead battery in a smart key or keyless entry fob, or a fault in the Anti-Theft system itself.

Bad fuel pump (Pump should run for a few seconds when ignition key is turned to start, no buzz means no fuel delivery to the engine).

Bad fuel pump relay (Relay is energized by PCM to route power to fuel pump when ignition is on).

Bad inertia fuel shut-off safety switch (Shuts off fuel in an accident, may have been tripped by a severe jolt, press button to reset).

Open in wiring anywhere in fuel pump wiring circuit (power or ground). Problem may be at wiring connector on top of fuel tank (hard to reach!).

No gas in fuel tank (Check the fuel gauge, and keep in mind the gauge may not be reading accurately).

Bad gas (Contaminated with water or too much alcohol or diesel fuel). If you just filled up with gas and now your car won't start, suspect bad gas.

Plugged Fuel Filter (When was the filter last changed?). Replace the filter. If plugged with rust,k fuel tank may also need to be cleaned or replaced.

Plugged or Pinched Fuel Line (Inspect fuel lines under vehicle for damage).

Leaky Fuel Pressure Regulator (Controls fuel pressure to injectors, which is critical for starting and proper air/fuel mixture).

No power to Fuel Injectors (Due to faulty fuel injector relay, blown fuse, no input signal to PCM from crank position sensor or cam position sensor, or bad PCM driver circuit). Injectors should usually have power when key is on. PCM grounds other side of injector circuit to pulse the injectors.

Major vacuum leak (An open EGR valve, disconnected vacuum hose, PCV valve, etc, can create a large vacuum leak and allow too much air to be sucked into the engine. This will make the air/fuel mixture too lean and make the engine hard to start. Engine will usually idle rough if it does start.

IGNITION RELATED CAUSES OF "NO START"

Bad crankshaft position sensor or distributor pickup (Sends pulse signal to ignition module and/or PCM that is necessary to trigger the ignition coil(s)).

Bad ignition module (controls firing of ignition coil(s), may have an intermittent open in circuitry that causes loss of spark, hard starting or sudden stalling, usually when hot)

Bad ignition coil(s). Ignition coil creates high voltage to fire the spark plugs. On engines with a distributor, a bad coil will prevent spark at all the spark plugs. On engines with a distributor less ignition system or coil-on-plug ignition, a bad coil will only affect one or two cylinders depending on the appliacation. This may make the engine hard to start, but it will run on the remaining cylinders that are firing.

Cracks or carbon tracks inside distributor cap or on rotor (on older engines with distributors, cracks or carbon tracks allow spark to short to ground before it reaches the spark plugs). Same thing can happen in coil-on-plug ignition systems if cracks or carbon tracks inside coil tube.

Bad spark plug wires (if wet, cracked, burned or internal resistance exceeds specifications, can interfere with good spark and make engine hard to start).

Fouled spark plugs (if the electrodes are contaminated with deposits, spark may short to ground before jumping gap causing misfires. Can make engine hard to start and run poorly. If plugs are wet when removed, it means they are not firing or engine is flooded).

COMMON CAUSES OF NO COMPRESSION

Broken timing belt or chain (Belt failure will prevent the valves from opening. The engine will NOT run if the belt has broken, and it may have bent valves or other damage as a result of the belt breaking).

Broken camshaft (This can happen on an overhead cam engine if the engine has overheated, warped the head and seized the camshaft).

Plugged catalytic converter (Creates a restriction that causes exhaust backpressure to back up. Engine may start but usually dies within a minute or two)

Engine & Driveability Problems: 5 How To Find & Fix Coolant Leaks

How To Find & Fix Coolant Leaks

Coolant leaks can occur anywhere in the cooling system. Nine out of ten times, coolant leaks are easy to find because the coolant can be seen dripping, spraying, seeping or bubbling from the leaky component. The first symptom of trouble is usually engine overheating. But your car may also have a Low Coolant indicator lamp. If you suspect your vehicle has a coolant leak, open the hood and visually inspect the engine and cooling system for any sign of liquid leaking from the engine, radiator or hoses. The color of the coolant may be green, orange or yellow depending on the type of antifreeze in the system. You may also notice a sweet smell, which is a characteristic odor of ethylene glycol antifreeze.

The most common places where coolant may be leaking are:

 A worn seal on the water pump shaft can leak coolant.

Water pump -- A bad shaft seal will allow coolant to dribble out of the vent hole just under the water pump pulley shaft. If the water pump is a two-piece unit with a backing plate, the gasket between the housing and back cover may be leaking. The gasket or o-ring that seals the pump to the engine front cover on cover-mounted water pumps can also leak coolant. Look for stains, discoloration or liquid coolant on the outside of the water pump or engine.

 This radiator is badly corroded and is not worth fixing 

Radiator -- Radiators can develop leaks around upper or loser hose connections as a result of vibration. The seams where the core is mated to the end tanks is another place where leaks frequently develop, especially on aluminum radiators with plastic end tanks. On copper/brass radiators, leaks typically occur where the cooling tubes in the core are connected or soldered to the core headers. The core itself is also vulnerable to stone damage. Internal corrosion caused by old coolant that has never been changed can also eat through the metal in the radiator, causing it to leak.

Most cooling systems today are designed to operate at 8 to 14 psi. If the radiator can't hold pressure, your engine will overheat and lose coolant.

 Pinch hoses to check for age cracks, hardening, soft spots, blisters or bulges.

Hoses -- Cracks, pinholes or splits in a radiator hose or heater hose will leak coolant. A hose leak will usually send a stream of hot coolant spraying out of the hose. A corroded hose connection or a loose or damaged hose clamp may also allow coolant to leak from the end of a hose. Sometimes the leak may only occur once the hose gets hot and the pinhole or crack opens up.

Freeze plugs -- These are the casting plugs or expansion plugs in the sides of the engine block and/or cylinder head. The flat steel plugs corroded from the inside out, and may develop leaks that are hard to see because of the plug's location behind the exhaust manifold, engine mount or other engine accessories. On V6 and V8 blocks, the plugs are most easily inspected from underneath the vehicle.

Heater Core -- The heater core is located inside the heating ventilation and air conditioning (HVAC) unit under the dash. It is out of sight so you cannot see a leak directly. But if the heater core is leaking (or a hose connection to the heater core is leaking), coolant will be seeping out of the bottom of the HVAC unit and dripping on the floor inside the passenger compartment. Look for stains or wet spots on the bottom of the plastic HVAC case, or on the passenger side floor. Some Chrysler vehicles have a reputation for developing coolant leaks in the heater core, and repeat heater core failures. Some have found that an aftermarket copper/brass replacement heater core lasts longer in these applications than the original equipment aluminum heater core.

Intake Manifold gasket -- The gasket that seals the intake manifold to the cylinder heads may leak and allow coolant to enter the intake port, crankcase or dribble down the outside of the engine. Some engines such as General Motors 3.1L and 3.4L V6 engines as well as 4.3L, 5.0L and 5.7L V8s are notorious for leaky intake manifold gaskets. The intake manifold gaskets on these engines are plastic and often fail at 50,000 to 80,000 miles. Other troublesome applications include the intake manifold gaskets on Buick 3800 V6 and Ford 4.0L V6 engines.

INTERNAL COOLANT LEAKS

There are the worst kind of coolant leaks for two reasons. One is that they are impossible to see because they are hidden inside the engine. The other is that internal coolant leaks can be very expensive to repair.

Bad head gasket --Internal coolant leaks are most often due to a bad head gasket. The head gasket may leak coolant into a cylinder, or into the crankcase. Coolant leaks into the crankcase dilute the oil and can damage the bearings in your engine. A head gasket leaking coolant into a cylinder can foul the spark plug, and create a lot of white smoke in the exhaust. Adding sealer to the cooling system may plug the leak if it is not too bad, but eventually the head gasket will have to be replaced.

If you suspect a head gasket leak, have the cooling system pressure tested. If it fails to hold pressure, there is an internal leak. A "block tester" can also be used to diagnose a leaky head gasket. This device draws air from the cooling system into a chamber that contains a special blue colored leak detection liquid. Combustion gases will react with the liquid and cause it to change color from blue to green if the head gasket is leaking.

Head gasket failures are often the result of engine overheating (which may have occurred because of a coolant leak elsewhere in the cooling system, a bad thermostat, or an electric cooling fan not working). When the engine overheats, thermal expansion can crush and damage portions of the head gasket. This damaged areas may then start to leak combustion pressure and/or coolant.

 A cracked cylinder head can leak coolant inside the engine.

Cracked Head or Block -- Internal coolant leaks can also occur if the cylinder head or engine block has a crack in a cooling jacket. A combustion chamber leak in the cylinder head or block will leak coolant into the cylinder. This dilutes the oil on the cylinder walls and can damage the piston and rings. If the coolant contains silicates (conventional green antifreeze), it can also foul the oxygen sensor and catalytic converter. If enough coolant leaks into the cylinder (as when the engine is sitting overnight), it may even hydro-lock the engine and prevent it from cranking when you try to start it. Internal leaks such as these can be diagnosed by pressure testing the cooling system or using a block checker.

A coolant leak into the crankcase is also bad news because it can damage the bearings. Coolant leaking into the crankcase will make the oil level on the dipstick appear to be higher than normal. The oil may also appear frothy, muddy or discolored because of the coolant contamination.

Leaky ATF oil cooler -- Internal coolant leakage can also occur in the automatic transmission fluid oil cooler inside the radiator. On most vehicles with automatic transmissions, ATF is routed through an oil cooler inside the radiator. If the tubing leaks, coolant can enter the transmission lines, contaminate the fluid and ruin the transmission. Red or brown drops of oil in the coolant would be a symptom of such a leak. Because the oil cooler is inside the radiator, the radiator must be replaced to eliminate the problem. The transmission fluid should also be changed.

PRESSURE TESTING THE COOLING SYSTEM FOR LEAKS

There are several ways to find out whether or not your cooling system is holding pressure. One is to top off your cooling system, tighten the radiator cap and start the engine. When the engine reaches normal operating temperature, turn on the air conditioner (to increase the cooling load on the system) and/or take it for a short drive. Then check the radiator, hoses and water pump for seepage or leaks.

WARNING: DO NOT open the radiator cap while the engine is hot! Even if the cooling system is leaking, the coolant will be under considerable pressure -- especially if it is low and coolant is boiling inside the engine. Shut the engine off and let it sit about an hour so it can cool down. Then place a rag over the radiator cap and slowly turn the cap until it starts to release pressure. Wait until all the pressure has vented before turning the cap the rest of the way off.

 Radiator pressure test kit

A special tool called a pressure tester can also be used to check your cooling system. The tool is nothing more than a little hand pump with a combination vacuum-pressure gauge and a fitting that is attached to the radiator filler neck. To check for leaks, attach the tool to the radiator and pressurize the radiator to the pressure rating on the radiator cap. For example, if you have a radiator cap that says 12 pounds, you pressurize the radiator to 12 lbs. and wait to see what happens. If there are no leaks, the system should hold pressure for 10 to 15 minutes. If it does not hold pressure, the system is leaking. If you cannot see any visible leaks on the outside, it means the leak is inside (bad head gasket or cracked head or block). 

A block Checker is another tool that can be used to detect a leaky head gasket. The gas-sensitive blue liquid changes color if there are any combustion gases in the coolant.

Leak detection dye can also be added to the coolant itself to make a slow leak easier to find. Some of these dyes glow bright green or yellow when exposed to ultraviolet light.

RADIATOR CAP CHECKS

The radiator cap should also be pressure tested, especially if the system has been overheating or losing coolant with no obvious external leaks. A weak cap that cannot hold pressure will allow the system to boil over. If the cap cannot hold its rated pressure, replace it.

 The best fox for a leaky radiator is to replace it with a new or recored radiator.

REPAIRING A LEAKY RADIATOR

If your radiator is leaking, you have several repair options:

You can try the cheap fix and add a bottle of cooling system sealer to the radiator. These products are designed to seal small leaks. They can also seal internal engine leaks. Some work better than others, but most provide only a temporary solution to your problem.

You can attempt to repair the radiator yourself. Copper/brass radiators on older vehicles can often be soldered to repair leaks. Cracks or pinholes in aluminum radiators in newer vehicles can often be repaired with epoxy glue. But if the core is severely corroded or damaged, the radiator may have to be professionally repaired at a radiator shop, or replaced with a new radiator.

HOW TO FIX A LEAKY HEATER CORE

As with a leaky radiator, you might try the cheapest fix and add a bottle of cooling system sealer to see if that will stop the leak. If the leak is small, the sealer will probably stop the leak - at least temporarily. But if the sealer does not stop the leak, you will have to disassemble the HVAC case to replace the heater core. This is a very time-consuming and difficult job that involves a LOT of labor on most vehicles. The labor to replace a heater core can often run 8 to 10 hours or more!

Some vehicles have had problems with repeat heater core failures (some Chrysler cars, for example). The problem in some cases is the design of the heater core itself, or the metal alloys from which it was made. But a common cause of heater core leaks is Electrolysis Corrosion. One fix is to attach a grounding strap on the heater core. Another is to replace an original equipment aluminum heater core with an aftermarket copper/brass heater core.

COOLANT RESERVOIR LEAKS

Another cooling system component that sometimes needs attention is the coolant overflow reservoir. The coolant overflow reservoir does more than catch the overflow from the radiator. It serves as a storage tank for excess coolant. When the system is hot, coolant will be forced out through the radiator pressure cap and into the reservoir. Then as the system cools down, decreasing pressure will draw coolant back into the radiator.

On many newer vehicles, the coolant reservoir is pressurized and is an integral part of the cooling system. The filler cap for the cooling system is located on the reservoir tank, and the tank is connected to the radiator and engine with hoses. The reservoir is transparent plastic and you can see the coolant level inside.

If the coolant reservoir is cracked or leaking, the system may lose coolant every time the engine heats up. Eventually, this can cause the engine to overheat.

Small punctures or cracks in the overflow reservoir can usually be repaired with silicone sealer. If the reservoir needs to be replaced, make sure the hoses are routed correctly between the radiator and the reservoir, and that it is free from kinks that could block the flow of coolant back and forth.

HOW TO FIX A LEAKY FREEZE PLUG

Freeze plus (also called expansion plugs) are round metal plugs that are pressed into cylinder head and engine block castings. The plug is supposed to push out and save the casting if the coolant does not contain enough antifreeze to prevent it from freezing during cold weather. Over time, the plugs can corrode from the inside and leak, causing the engine to lose coolant and overheat.

One way to temporarily patch a leaky freeze plug is to clean the surface of the plug, sand it lightly with sandpaper, and pack it solid with a high temperature two-part epoxy such as gas tank sealer or JB Weld epoxy. Let it cure overnight. This trick usually seals leaky expansion plugs that would otherwise be very difficult to replace.

To replace a leaky freeze plug, use a hammer and drift to knock out the old plug. Pounding in on one side of the plug will usually cause it to twist. The plug can then be pried out with a large screwdriver. Clean the hole, then apply a liberal coating of sealer to the hole and carefully drive in a new replacement plug. The plug must go in straight or it may not seal.

Another repair option is to replace a solid metal freeze plug with an expandable freeze plug. The expandable plugs have a rubber grommet that expands and seals against the opening when the center bolt in the plug is tightened. It's easier to install and less apt to leak than a solid plug.

HOW TO FIX A LEAKY COOLANT HOSE

Do not waste your time trying to patch or wrap a leaky radiator or heater hose. Sealers and Stop Leak products also do not work well with hoses. Replace the bad hose with a new one, and inspect all the other hoses because if one has failed the others are probably reaching the end of the road, too.

Old hoses are often hard and stick to their fittings, making them difficult to remove. Use a razor blade or box cutter to slit the old hose so it can be easily pulled off its end fittings.

It is also a good idea to replace the original hose clamps, especially if they are the ring type. Ring clamps can lose tension with age and may not hold the hose tightly. Worm drive stainless steel clamps are best. But quality brand stainless steel worn drive clamps, not the cheap plain steel ones that are made in China. They will rust and fail.

You should also inspect the inside of your old radiator and heater hoses after they have been removed to check for deep fissures or cracks caused by Electrolysis Corrosion. This type of corrosion can be caused by old antifreeze that no longer provides adequate corrosion protection, or by stray electrical currents that use the coolant as a ground path.

HOW TO FIX A LEAKY WATER PUMP

No Stop Leak or cooling system sealer product will seal a water pump that is leaking coolant past the shaft seal. Replacement is your only option. But you can save some money on the job by using a remanufactured water pump rather than a new water pump.

Replacing a water pump is not too hard a job on most engines, but on some it can be tricky. On some engines (2.8L GM V6 engines, for example), the bolts that hold the water pump also hold the timing cover in place. If you are not careful, the timing cover seal can be broken allowing coolant to leak into the crankcase. GM recommends using a special tool (J-29176 or equivalent) to hold the timing cover tight while the pump is being changed.

 Check the fan clutch because a weak clutch can cause the engine to overheat.

If your engine has a belt-driven fan with a fan clutch, it is also a good idea to check the fan clutch when replacing the water pump. The lifespan of both is about the same, so the fan clutch may also need be replaced. If the clutch is leaking silicone fluid, or has any wobble in the bearing, it must be replaced.

REFILLING THE COOLING SYSTEM

When refilling the cooling system after making a repair, always use a 50/50 mixture of antifreeze and water. Never use straight water because it has no freezing protection, no corrosion protection and it boils at a lower temperature (212 degrees F.) than a mixture of antifreeze and water (which protects to 240 degrees F.).

Use the type of antifreeze specified by the vehicle manufacturer, or a Universal Coolant that is compatible with all makes/models. Most late model vehicles require some type of OAT or HOAT long life coolant. GM vehicles use Dex-Cool.

On some late model front-wheel drive cars, refilling the cooling system can be tricky unless you "burp" the system by opening a bleeder vent or cracking a hose at a high point in the system to allow trapped air to escape. If you do not get all of the air out, the engine may overheat the first time you drive it.

The best way to refill the system is to add coolant until the radiator is within an inch of being full. Also add coolant to the coolant reservoir, filling it to the proper level. If the system has a pressurized coolant reservoir, add coolant until the level inside the reservoir is at the COLD FULL mark. Start the engine and let it idle with the radiator or coolant reservoir cap off until the thermostat opens and coolant starts to circulate through the engine. The heater should also be on so coolant will flow through the heater core. As the coolant level drops, continue to add coolant until the system takes no more. Then replace the radiator cap and drive a short distance. Shut the engine off, and after it has cooled recheck the coolant level once again. If low, add as needed.

Engine & Driveability Problems: 4 Engine Overheating

Engine Overheating

Is your engine overheating? Most engines are designed to operate within a "normal" temperature range of about 195 to 220 degrees F. A relatively constant operating temperature is essential for proper emissions control, good fuel economy and performance. But problems can arise that cause the engine to run hotter than normal, resulting in engine overheating.

Your engine's cooling system is filled with a 50/50 mixture of water and ethylene glycol antifreeze. The coolant will boil at 225 degrees unless it is held under pressure by the radiator cap. A 15 PSI radiator cap will increase the boiling temperature of a 50/50 coolant blend up to 265 degrees F. If the concentration of antifreeze to water is upped to 70/30 (the maximum recommended), the boiling temperature with a 15 psi radiator cap goes up to 276 degrees. So obviously the radiator cap plays a significant role in preventing the coolant from boiling and the engine from overheating.

Anytime temperatures climb beyond the normal range, for any reason, your engine is in danger of overheating.

POSSIBLE CAUSES OF OVERHEATING

Overheating can be caused by anything that decreases the cooling system's ability to absorb, transport and dissipate heat: A low coolant level, a coolant leak (through internal or external leaks), poor heat conductivity inside the engine because of accumulated deposits in the water jackets, a defective thermostat that doesn't open, poor airflow through the radiator, a slipping fan clutch, an inoperative electric cooling fan, a collapsed lower radiator hose, an eroded or loose water pump impeller, or even a defective radiator cap.

One of nature's basic laws says that heat always flows from an area of higher temperature to an area of lesser temperature, never the other way around. The only way to cool hot metal, therefore, is to keep it in constant contact with a cooler liquid. And the only way to do that is to keep the coolant in constant circulation. As soon as the circulation stops, either because of a problem with the water pump, thermostat or loss of coolant, engine temperatures begin to rise and the engine starts to overheat.

The coolant also has to get rid of the heat it soaks up inside the engine. If the radiator is clogged with bugs and debris, or if its internal passages are blocked with sediment, rust or gunk, the cooling efficiency will be reduced and the engine will run hot. The same thing will happen if the cooling fan is not engaging or spinning fast enough to pull air through the radiator.

The thermostat must be doing its job to keep the engine's average temperature within the normal range so the engine does not overheat. If the thermostat fails to open, it will effectively block the flow of coolant and the engine will overheat.

Exhaust restrictions can also cause the engine to overheat. The exhaust carries a lot of heat away from the engine, so if the catalytic converter is restricted, or a pipe has been crimped or crushed, exhasut flow can be restrricted causing heat to build up inside the engine.

It's also possible that your engine really isn't overheating at all. Your temperature gauge or warning lamp might be coming on because of a faulty coolant sensor. Sometimes this can be caused by a low coolant level or air trapped under the sensor.

POSSIBLE CONSEQUENCES OF ENGINE OVERHEATING

If your engine is overheating, it may start to detonate. The engine may rattle and ping and lose power. If detonation continues, it may damage the rings, pistons and/or rod bearings.

Overheating can also cause pisto scuffing. As the engine gets hotter and hotter, the pistons may swell to the point where there is no more room for expansion and they scrape against the cylinders, damaging the pistons and cylinders.

Exhaust valves may also stick or scuff in their guides. This can damage the valves, guides and lead to a loss of compression.

Another consequence of engine overheating may be a blown head gasket. Heat makes aluminum swell almost three times faster than cast iron. Thermal stress can distort the head and make it swell in areas that are hottest like those between exhaust valves in adjoining cylinders, and areas that have restricted coolant flow like the narrow area that separates the cylinders. The typical aluminum head swells most in the middle, which can crush the head gasket if the head gets too hot. This will usually cause the head gasket to leak compression between adjacent cylinders, or leak coolant into the cylinders.

Engine overheating can also cause an overhead cam to seize and break.

Engine overheating may also stress old radiator and heater hoses and cause they to burst under the additional pressure. Steam that is generated inside the cooling system can also damage radiators with plastic end tanks.

A HOT warning lamp should never be ignored. Though a few high tech cars like Cadillacs with the Northstar engine can disable cylinders to "air-cool" the engine and keep it running at reduced power in the event of coolant loss, most engines will suffer serious damage if they overheat. So advise your customers to stop driving at the first sign of overheating. Turn the engine off, let it cool down and try to find and fix the cause before risking further travel.

WHAT TO CHECK

* Bad Thermostat -- Severe engine overheating can often damage a good thermostat. If the engine has overheated because of another problem, therefore, the thermostat should be tested or replaced before the engine is returned to service.

One way to check the thermostat is to start the engine and feel the upper radiator hose (or use an infrared noncontact thermometer to read its temperature). The hose should not feel uncomfortably hot until the engine has warmed-up and the thermostat opens. If the hose does not get hot, it means the thermostat is not opening.

Another way to test the thermostat is to remove it and dip it into a pan of boiling water (it should open). The exact opening temperature can be checked by using a thermometer.

If the thermostat needs to be replaced, install one with the same temperature rating as the original. Most cars and light trucks since 1971 require thermostats with 192 or 195 degree ratings. Using a cooler thermostat (160 or 180) in an attempt to "cure" a tendency to overheat can increase fuel and oil consumption, ring wear and emissions. On newer vehicles with computerized engine controls, the wrong thermostat can prevent the computer system from going into closed loop resulting in major performance and emission problems if the engine fails to reach its normal operating temperature.

TIP: When refilling the cooling system, air can become trapped under the thermostat. This will form a steam pocket that prevents the thermostat from opening and may cause the engine to overheat. Some cooling systems have one or more bleeder valves that can be opened to vent air from the system while refilling the system. If your cooling system does not have a bleeder valve, you can drill a small hole in the thermostat as shown. This will allow air to escape past the thermostat so it is not trapped inside the engine block. Some thermostats come with a similar feature called a "jiggle valve." There is a small hole in the thermostat with a pin that allows air to escape.

* Cooling system leaks -- Loss of coolant because of a coolant leak is probably the most common cause of engine overheating. Possible leak points include hoses, the radiator, heater core, water pump, thermostat housing, head gasket, freeze plugs, automatic transmission oil cooler, cylinder head(s) and block.

Make a careful visual inspection of your entire cooling system, and then PRESSURE TEST the cooling system and radiator cap. A pressure test will reveal internal leaks such as seepage past the head gasket as well as cracks in the head or block. A good system should hold 12 to 15 psi for 15 minutes or more with no loss in pressure. If it leaks pressure, there is an internal coolant leak (most likely a bad head gasket but possibly also a cracked cylinder or engine block).

It is important to pressure test the radiator cap, too, because a weak cap (or one with too low a pressure rating for the application) will lower the coolant's boiling point and can allow coolant to escape from the radiator.

Leaky Head Gasket -- Bad news because repairs are expensive. A leaky head gasket can allow coolant to seep into the engine's cylinders or crankcase. Symptoms include a loss of coolant with no visible external leaks, and white steam in the exhaust, especially after restarting the engine when it has sit for awhile. A leaky head gasket can be diagnosed by pressure testing the cooling system, or by using a "block checker" that pulls air from the cooling system into a cylinder that contains a special blue colored leak detection liquid. If there are any combustion gases in the coolant, the color of the liquid inside the detector will change from blue to green. A leaky head gasket can often be temporarily sealed by adding a sealer product to the cooling system. But for bad leaks or ones that cannot be stopped with sealer, the head gasket has to be replaced.

Fan Not Working -- With mechanical fans, most engine overheating problems are caused by a faulty fan clutch, though a missing fan shroud can reduce the fan's cooling effectiveness by as much as 50% (depending on the fan's distance from the radiator) which may be enough to cause the engine to overheat in hot weather or when working hard.

Defective fan clutches are a common and often overlooked cause of engine overheating. The shear characteristics of the clutch fluid gradually deteriorates over time, with an average loss in drive efficiency of about 200 rpm per year. Eventually slippage reaches the point where effective cooling is no longer possible and overheating results. (On average, the life of a fan clutch is about the same as a water pump. If one needs to be replaced, the other usually does too.)

If the fan clutch shows signs of fluid leakage (oily streaks radiating outward from the hub of the clutch), spins freely with little or no resistance when the engine is off, or wobbles when the fan is pushed in or out, it needs to be replaced.

With an electric cooling fan, check to see that the fan cycles on when the engine gets hot and when the air conditioner is on. If the fan fails to come on, check the fan motor wiring connections, fan relay and temperature sensor. Try jumping the fan directly to the battery. If it runs, the problem is in the wiring, relay or sensor. If it fails to run, the fan motor is bad and needs to be replaced.

With a hydraulic cooling fan, the fan must be turning fast enough to provide adequate cooling at idle and low speed.

Leaky Water pump -- Any wobble in the pump shaft or seepage would call for replacement. In some instances, a pump can cause an engine to overheat if the impeller vanes are badly eroded due to corrosion or if the impeller has come loose from the shaft. The wrong pump may also cause an engine to overheat. Some engines with serpentine drive belts require a special water pump that turns in the opposite direction of those used on the same engine with ordinary V-belts.

 Cavitation damage inside a water pump

It does not happen very often, but sometimes the water pump impeller can loosen up on the pump shaft and not turn, although the water pump pulley appears to be turning normally. If the impeller does not spin, there will be little or no circulation of coolant through the engine. The only way to know if this is the problem is to remove the water pump and check the impeller to see that is is tight on the shaft. Also, some plastic impellers can become severely eroded over time. The water pump housing and/or impeller may also experience cavitation erosion. The loss of blade area or an increase in clearance between the housing and impeller will reduce the flow of coolant and can lead to engine overheating.

Slipping Belt -- Check belt tension and condition. A loose belt that slips may prevent the water pump from circulating coolant fast enough and/or the fan from turning fast for proper cooling.

Lower Radiator Hose Collapsing -- A pinched hose (upper or lower) or a lower radiator hose that is collapsing and blocking the flow of coolant when the engine is running can cause engine overheating. The lower hose usually has a metal reinforcing wire inside that looks like a large spring. It s purpose is to prevent the hose from collapsing when the water pump is pulling water through the hose. If this wire is missing or has failed due to corrosion, the hose may collapse.

Plugged or Dirty Radiator -- Dirt, dead bugs and debris can block air flow through the radiator and reduce its ability to dissipate heat. Internal corrosion and an accumulation of deposits can also block the flow of coolant. A good way to find internal clogs is to use an infrared thermometer to "scan" the surface of the radiator for cold spots. If clogged, the radiator should be removed for cleaning or replaced. Backflushing the cooling system and/or using chemical cleaners can remove rust and hard water scale, but may do little to open up a clogged radiator.

When refilling the cooling system, be sure you get it completely full. Air pockets in the head(s), heater core and below the thermostat can interfere with proper coolant circulation and cooling. If the cooling system has no bleeder valves to vent air, you may have to temporarily loosen a heater hose to get all the air out of the system.

Excessive exhaust backpressure -- A clogged catalytic converter will restrict the flow of exhaust and cause heat to back up in the engine. Other causes include a crushed exhaust pipe or a collapsed double wall pipe. Check intake vacuum at idle. If intake vacuum reads low and continues to drop, inspect the exhaust system.

Overheated incoming air -- On older vehicles with a carburetor or throttle body injection, check the operation of the heated air intake system on the air cleaner. If the temperature control valve is stuck so only heated air from around the exhaust manifold is drawn into the air cleaner, it may contribute to detonation and/or engine overheating. Also check the heat riser valve for manifold heat on older V6 and V8 engines. If stuck shut, it may be overheating the intake manifold.

Dragging brakes -- A disc brake caliper that is sticking or a parking brake that is not releasing may be making your engine work harder than normal to overcome the friction. Check the brakes and fix as needed.

Overworking the engine -- The cooling systems in many passenger cars today are marginal and have little excess capacity to handle extra heat generated by towing or high speed mountain driving in hot weather. Replacing the original stock radiator with a larger or thicker radiator can improve cooling capacity.

Engine & Driveability Problems: 3 Engine Temperature Warning Light

Engine Temperature Warning Light

Should You Continue Driving If Your Temperature Warning Light is On?

Driving with the temperature warning light on can increase the risk expensive engine damage! When the temperature light comes on, it means your engine is overheating (running too hot). An engine should not overheat if the cooling system is properly filled and is working normally -- even during hot weather or stop-and-go driving. Sometimes abnormal driving conditions such

as towing a heavy trailer during hot weather may overload the cooling system's capacity to control heat, but usually, a temperature warning light means trouble.

What To Do If Your Temperature Warning Light Comes On

STOP DRIVING IMMEDIATELY!. Pull over to the side of the road as soon as it is safe to do so, then shut off your engine and wait for things to cool down.

WARNING: Do NOT attempt to open the radiator cap! The radiator contains hot water under high pressure. Opening the cap on the radiator or a pressurized coolant reservoir could allow steam and water to blow out and burn you. There's nothing to be accomplished by opening the cap while the engine is still hot, so let your vehicle sit and cool off.

After things have cooled down (wait at least half an hour or more), then you can open the radiator cap or reservoir and check the coolant level. Place a rag over the cap first, and slowly turn the cap until it stops at the first detent. This should allow residual pressure to be released. Wait until all pressure has been released before removing the cap the rest of the way.

Add water or coolant to the radiator or coolant reservoir if it is low. Actually, you should add premixed coolant or a 50/50 mixture of antifreeze and water to maintain the proper freezing, boil over and corrosion protection. But in most cases when this happens, it's an emergency situation and you won't have a jug of antifreeze handy. If that's the case, add water now, then drain out some of the coolant later and offset the extra water by adding the proper amount of antifreeze.

Check for Coolant Leaks

Your engine may have overheated because of a coolant leak. Visually inspect the radiator, engine and cooling system for leaks. Common leak points include radiator and heater hoses, hose connections, the water pump and radiator. Internal leaks (such as a crack in the head or engine) can't be seen and can only be diagnosed by pressure testing the cooling system.

IF YOU DON'T STOP DRIVING...

If you keep driving an engine that is overheating, it can cause serious damage. The engine may start to knock (caused by detonation), which in turn can cause piston, ring, and head gasket damage. As the internal parts of the engine expand from the excessive heat, clearances may be reduced to the point where metal-to-metal contact occurs. Valve stems may gall and stick, and the pistons and camshaft might scuff or seize.

Severe engine overheating also creates tremendous thermal stress in the head(s) and block. This, in turn, may lead to cracking and/or warpage. This is a common problem with overhead cam engines that have aluminum heads.

The only vehicle that can be "safely" driven when the temperature warning light is on a late model Cadillac with a Northstar V8 engine. Cadillac engineers designed the engine control system to automatically deactivate half of the engine's cylinders if it senses an overheating problem. This reduces the heat (and power) being generated by the engine, and it allows the "dead" cylinders to pump air through the engine for internal cooling. The system is designed to provide a "limp-in" mode so the vehicle can be driven to the nearest service facility or Cadillac dealer for repairs. It is not designed for continuous driving.

Engine & Driveability Problems: 2 Engine Oil Pressure Warning Light On

Engine Oil Pressure Warning Light On

Copyright AA1Car

If the engine oil pressure warning light is on, it may mean your engine has lost normal oil pressure. STOP driving immediately and turn the engine off. The engine can be severely damaged if oil pressure is lost.

Possible Causes of Low Oil Pressure Warning Light:

A low oil level (check the dipstick), bad oil pump, or defective oil pressure sending unit, oil pressure gauge or warning light switch.

Oil Pressure Warning Light Diagnosis

First, determine if the oil is full or low by checking the dipstick. NOTE: On some engines, there is an oil level sensor in the engine's oil pan that will turn on the oil warning light if the oil level is low. If the dipstick shows a low oil level (the oil level is at or below the ADD line, or no oil can be seen on the dipstick), your engine may be leaking oil, burning oil or both.

Oil leaks are a common cause of oil consumption and a low oil level in the engine. Oil leaks can occur at the valve cover, oil pan or timing cover gaskets, or the front and rear crankshaft oil seals. Inspect the top, sides and bottom of the engine for signs of oil leakage. Look for greasy stains, heavy accumulations of grease, or oil dripping on the ground. The higher the miles on the engine, the more likely the gaskets and seals may be leaking. If your engine is leaking oil because of a bad gasket or seal, the leaky gasket or seal should be replaced.

If the outside of the engine is clean and there are no obvious oil leaks, and the oil level is low, the engine is probably burning oil due to worn piston rings, valve guides or valve guide seals. This may be the result of high mileage wear or neglect. Either way, this kind of oil consumption problem is expensive to fix because it may require rebuilding or replacing the engine. NOTE: On many engines, replacing the valve guide seals will significantly reduce oil burning if the original guides and seals are worn.

If the oil usage is not too severe (say less than one quart of oil every 1000miles), check the dipstick often and keep adding oil as needed. If the engine is using a lot of oil (say more than a quart every 500 miles), check the dipstick constantly and keep plenty of oil on hand. An engine that is burning a lot of oil is worn out and will soon have to be overhauled or replaced.

Bad Oil Pump?

If the oil level is between ADD and FULL, and the engine was making noise when it was running, the problem may be a bad oil pump. DO NOT run the engine until the problem can be repaired. Oil pressure can be checked by attaching a pressure gauge to the engine where the oil pressure sending unit is attached. If oil pressure is within specifications (typically 10 psi for every 1000 rpm) the oil pump is okay. If pressure is less than specifications, the oil pump may be worn, or the engine bearings may be worn.

If the oil level is between ADD and FULL, and the engine was running normally (no noise) after the oil pressure warning light came on, the problem may be a defective oil pressure sending unit, oil pressure gauge or warning light switch. You can probably start the engine and drive the vehicle home or to a shop for repairs. But if the engine starts to become noisy, STOP and shut off the engine.

Low Oil Pressure Fixes

If the oil level is low, add oil to the engine to bring the level up to the FULL mark on the dipstick. DO NOT overfill the crankcase. Use the type of oil viscosity specified in the vehicle owners manual.

If the oil pressure gauge reading remains low or the oil pressure warning light remains on, remove the oil pressure sending unit on the engine and connect a pressure gauge directly to the engine. Start the engine to see if the pump is generating adequate pressure. If pressure is normal (about 10 PSI for every 1000 RPMs of engine speed, the problem is not a bad oil pump, but a faulty oil pressure sending unit. Replace the oil sending unit.

If you do not have a pressure gauge for testing oil pressure, try replacing the oil pressure sending unit with a new one. If the oil pressure warning light goes out or the gauge reading is now normal, you have fixed the problem. But if the warning light or low gauge reading continues, the problem is likely a bad oil pump.

If the oil pump is bad (does not produce adequate pressure), the oil pump will have to be replaced. On many engines, the oil pump is located inside the oil pan on the bottom of the engine. The pan must be removed to replace the pump. This may require raising the engine and/or removing steering or suspension components that are in the way so the pan can be removed. On other engines, the oil pump is located inside the timing cover on the front of the engine. Disassembly requires removing most of the components on the front of the engine to access the pump. This type of pump is much more difficult and time consuming to replace.

If oil pressure is low because of worn engine bearings, the crankshaft bearings will have to be replaced. This usually requires overhauling or replacing the engine.

Engine & Driveability Problems: 1 Check Engine Light On

Check Engine Light On

The Check Engine Light (which is actually the Malfunction Indicator Lamp or MIL) alerts you when an emissions-related problem occurs with the engine control system or emission controls on your vehicle. Depending on the nature of the problem, the Check Engine Light may come on and remain on continuously or flash. Some intermittent problems will make the Check Engine Light come on only while the fault is occurring (such as engine misfire). The Check Engine light usually remains on once a fault has been detected, and will remain on to remind you that a problem has occurred that needs to be investigated.

An illuminated Check Engine Light can be annoying because you don't know what's wrong, and whether or not the problem might be a serious one or just a minor fault. There is no way to know what the problem is until you plug a scan tool into the vehicle's diagnostic connector and read out the code(s) that turned the light on.

If no other warning lights are on, and the engine seems to be running normally (no unusual noises, smells, vibrations, etc.), you can assume the fault that is causing the Check Engine Light to come on is probably minor and won't hinder your ability to continue driving. But if other warning lights are on, you should probably stop and investigate the problem.

When the Check Engine Light comes on, a diagnostic trouble code (DTC) is recorded in the powertrain control module (PCM) memory that corresponds to the fault. Some problems can generate more than one trouble code, and some vehicles may have multiple problems that set multiple trouble codes.

CHECK ENGINE LIGHT ON SETS TROUBLE CODES

In most older vehicles (those made before 1996), disconnecting the computer's power source or disconnecting a battery cable erases fault codes and turns off the Check Engine Light, at least temporarily. If the problem persists, the code will reset and the Check Engine Light will come back on. But on many newer vehicles, you do NOT want to disconnect the battery because doing so can wipe out the computer's memory settings. This may affect the operation of the transmission, climate control system, and other functions.

In 1996 and newer vehicles, a scan tool or code reader must be used to erase codes and turn the Check Engine Light off.

 

HOW TO READ FAULT CODES WITH A SCAN TOOL

If your Check Engine light is on, you need to read the code(s) that are causing it to come on with a code reader or scan tool. Plug the tool into the 16-pin OBD diagnostic connector (usually located under the dash near the steering column).

When the ignition is turned on (don't start the engine yet), the tool will communicate with the PCM. You may be asked to enter the year/make/model and VIN code of your vehicle if the scan tool does not automatically recognize the application. Choose the READ FAULT CODE option on the scan tool menu, or press the button that allows the tool to read the codes. The tool will then display a number and/or code description that corresponds to a particular fault code. The letter "P" is the designation for Powertrain codes (which includes all of the engine controls, related emission controls, catalytic converter and fuel tank vapor control system). If there are more than one code, the codes will be listed in numeric order.

TIP: Write the code(s) down on a piece of paper before you erase them. You may need to refer to the codes again later if the same problem keeps returning. Erasing the codes will turn the Check Engine Light off, but sooner or later the codes will likely return and turn the Check Engine Light back on again if the problem is still there.

Important! A fault code will tell you which sensor or system experienced some kind of problem. But the code will NOT tell you why the fault occurred, how bad the fault is or which part to replace. That usually requires more advanced diagnostics.

CHECK ENGINE LIGHT ON DIAGNOSTICS

Prior to OBD II, fault detection was mostly limited to "gross failures" within individual circuits or sensors. The first generation systems were not capable of detecting misfire, converter problems or fuel vapor leaks. OBD II changed all of that by adding the ability to monitor these things so emission problems can be detected as they develop.

OBD II uses the Check Engine Light to alert the driver when a fault occurs, and it stores trouble codes that correspond to specific kinds of problems. It can also track problems as they develop and even capture a snapshot of sensor data when a problem occurs.

Almost any emission problem that causes hydrocarbon emissions to exceed 1.5 times the federal limit can cause the Check Engine Light to come on with OBD II, even if there is no noticeable driveability problem accompanying the emission problem.

OBD II not only monitors the operation of all the engine's sensors and systems (fuel, ignition, EGR, evaporative emissions, etc.), it also monitors the operation of the catalytic converter and can even detect engine misfires! Anything that could possibly affect emissions is monitored by OBD II, including a loose gas cap! 

UNDERSTANDING DIAGNOSTIC TROUBLE CODES

A misfire will cause the Check Engine Light to flash while the misfire is occurring. A misfire that occurs in a given cylinder will also set a P030X code where "X" will be the number of the cylinder that is misfiring. For example, a P0302 code would tell you cylinder number two is misfiring. Remember, the code does not tell you why the cylinder is misfiring. You have to figure that out by performing other diagnostic tests. The misfire might be due to a fouled spark plug, a bad plug wire, a defective ignition coil in a DIS ignition system, a clogged or dead fuel injector or a loss of compression due to a leaky exhaust valve, leaky head gasket or worn cam lobe.

OBD II monitors the operating efficiency of the catalytic converter with a second oxygen sensor in the tailpipe behind the converter. By comparing upstream and downstream O2 sensor readings, it can determine how well the converter is doing its job. If converter efficiency drops below a certain threshold, OBD II will set a code and turn on the Check Engine Light.

OBD II can detect fuel vapor leaks (evaporative emissions) in the charcoal canister, evap plumbing or fuel tank by pressurizing or pulling a vacuum on the fuel system. If the gas cap is loose or missing, it will detect it, set a code and turn on the Check Engine Light.

In addition, OBD II can also generate codes for various electronic transmission problems and even air condition failures such as a compressor failure.

TWO KINDS OF FAULT CODES

OBD II is capable of generating two types of diagnostic trouble codes: "Generic" or "Global" codes (P0) that are the same for all makes and models of vehicles (these are required by law), and "Enhanced" or "OEM" codes (P1) that are unique to specific vehicles. Enhanced codes can also cover non-emission related failures that occur outside the engine control system. These include ABS codes, HVAC codes, airbag codes and other body and electrical codes.

The "generic" codes that are common to all vehicle manufacturers can be accessed using any basic code reader or scan tool that is OBD II compliant. Unfortunately, most older scan tools made before 1995 won't work on 1996 and newer vehicles with OBD II. You need a scan tool that has the proper hardware and software to talk to your onboard computer so it can read OBD II codes and other diagnostic information. In fact, a scan tool or code reader is required to read codes on most 1996 and newer vehicles because most newer vehicles do not have manual flash codes. There are some exceptions. Some Nissan models still provide manual flash codes, as do some Dodge models. Most GM, Ford, Honda and Toyota models do not have flash codes, but on some GM vehicles with a driver information display, there may be a procedure for displaying codes manually.

A simple code reader that plugs into the vehicle diagnostic connector can usually be purchased at an auto parts store for under $60. A basic scan tool that can read codes and additional system data (and erase codes) may sell for $70 to $400 depending on its features. The kind of scan tools that professional technicians use can cost several thousand dollars and have more advanced features, including bidirectional capabilities that allow the scan tool to run various self-tests that are built into the engine management system on your vehicle. These types of advanced tests may be required for more difficult-to-diagnose problems. The high end professional level scan tools can also graph sensor voltages, allowing them to reveal diagnostic data that a simple DIY scan tool cannot.

If you do not have a code reader or scan tool, you will have to take your vehicle to a repair facility or auto parts store if you need to diagnose a Check Engine Light problem.

Money Saving Tip: Some parts stores (such as AutoZone and others) will do a FREE plug-in diagnosis for you, or they will loan you a scan tool so you can do the basic diagnosis yourself in the parking lot. The scan tool will tell you what the codes are that turned on your Check Engine Light. Just remember that a code by itself does NOT tell you which part may need to be replaced. Additional diagnostic tests are usually needed to determine the underlying cause that set the code.

For example, a P0300 Random Misfire Code means the engine is misfiring in multiple cylinders but it doesn't tell you why it is misfiring. The cause could be fuel, ignition or compression, or any combination thereof. Additional tests are needed to identify the cause of the misfire.

YOUR VEHICLE WILL NOT PASS AN OBD PLUG-IN EMISSIONS TEST WITH A CHECK ENGINE LIGHT ON

If your Check Engine Light is on, your vehicle will NOT pass an OBD plug-in emissions test. So if you are required to take such a test, the light must be out and there must be no codes in the PCM memory. You can't just erase the codes, drive your vehicle to the test station and take the test if the original problem is still there. The OBD II monitors need time to set, which usually requires driving at various speeds, sometimes over a period of several days. The OBD plug-in test checks to see if all of the monitor self-tests have completed, and if they have not your vehicle is rejected for not being ready.

The OBD plug-in test also determines if your Check Engine light is functioning properly. if the lamp is burned out or has been disabled, your vehicle will be rejected until the bulb is replaced or the problem has been fixed.

If the test finds any DTCs (Diagnostic Trouble Codes), your vehicle will fail the emissions test. The test center should give you a print out that lists any codes found along with possible suggestions as to what may be causing the fault(s). You must then have your vehicle repaired (which you can do yourself if you have the tools and know-how to do) or you can take it to a repair shop or new car dealer to have the problem fixed.