Defective thermostatic valve
Low compression
Loose battery terminals
Water in the fuel system
Clogged air cleaner
Clogged fuel filter
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
High air draft
High circulation of water
Radiator core blocked
High water level in radiator