Coolant level
Clogged oil filter
Clogged air cleaner
Weak compression
Oil level is high
Clogged air filter
Defective pressure release valve
Defective oil pump
Defective thermostat
Defective water pump
Defective starter motor
Engine does not crank
Abnormal noise in the engine
Engine back fire
Air lock in the fuel system
Low oil level
Oil filter clogged
Oil viscosity high
Worn-out valve guides