Clogged fuel filter
Fuel leakage
External leakage of oil
Defective thermostat valve
Defective thermostatic valve
Low compression
Loose battery terminals
Water in the fuel system
Clogged air cleaner
Worn out of piston rings
Low oil level
Clogged oil filter
Correct injection timing
More supply of fuel
More supply of air
Incomplete combustion of fuel
Defective oil filter