Troubleshooting
8-15
Engine Overheating
1. Improper spark plug heat range.
2. Low oil level.
3. Oil not circulating properly.
4. Valves leaking.
5. Heavy carbon deposits in the combustion chamber.
6. Dragging brake(s).
7. Slipping clutch.
Preignition
Preignition is the premature burning of fuel and is caused by hot spots in the
combustion chamber. Glowing deposits in the combustion chamber, inadequate Cooling
or an overheated spark plug can all cause preignition. This is first noticed as a power
loss but eventually causes damage to the internal parts of the engine because of the
high combustion chamber temperature.
Engine Noises
Unusual noises are often the first indication of a developing problem. Investigate any
new noises as soon as possible. Something that may be a minor problem, if corrected,
could prevent the possibility of more extensive damage.
Use a mechanic’s stethoscope or a small section of hose held near your ear (not
directly on your ear) with the other end close to the source of the noise to isolate the
location. Determining the exact cause of a noise can be difficult. If this is the case,
consult with a professional mechanic to determine the cause. Do not disassemble major
components until all other possibilities have been eliminated.
Consider the following when troubleshooting engine noises:
• Knocking or pinging during acceleration can be caused by using a lower octane
fuel than recommended. It may also be caused by poor fuel. Pinging can also be
caused by an incorrect spark plug heat range or carbon buildup in the
combustion chamber.
• Slapping or rattling noises at low speed or during acceleration—May be caused
by excessive piston-to-cylinder wall clearance (piston slap).
Note:
Piston slap is easier to detect when the engine is cold and before the piston has
expanded. Once the engine has warmed up, piston expansion reduces piston-to-
cylinder clearance.
• Knocking or rapping while decelerating. Usually caused by excessive rod bearing
clearance.
• Persistent knocking and vibration occurring every crankshaft rotation—Usually
caused by worn rod or main bearing(s). Can also be caused by broken piston
rings or a damaged piston pin.
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