Troubleshooting by Exhaust Color
This question deals with troubleshooting the condition of the combustion chamber by exhaust color. The combustion chamber requires the correct air fuel mixture as well as a tight seal for proper combustion.
Blue/Gray Smoke: Blue gray smoke is an indication of oil burning in the combustion chamber. These are possible symptoms and causes:
Valve Seals: Leaking valve seals will cause blue/gray smoke at startup, because gravity pulls oil past the seals into the cylinder after the engine is shut down.
Valve Guides: Excessive clearance between the valve stem and the valve guide will allow oil to leak past the gap into the cylinder.
Piston Rings: Worn or damaged piston rings will cause oil blowby resulting in blue/gray smoke.
Worn Cylinder Walls: Worn cylinder walls cause oil blowby resulting in blue/gray smoke.
PCV System: A stuck closed PCV system will cause excessive crankcase pressure resulting in blue/gray smoke.
Black Smoke: Black exhaust smoke is an indication of a rich fuel condition. These are possible causes:
Fuel Injectors: A leaking or dripping fuel injector will cause a rich fuel condition.
Fuel Pressure Regulator: A stuck closed fuel pressure regulator will cause a rich fuel condition.
Fuel Return: A restricted fuel return line will cause a rich fuel condition.
White/Gray Smoke: White exhaust smoke is an indication that coolant is burning in the combustion chamber. These are possible causes:
Cylinder Head: A crack in the cylinder head (around the coolant jacket) will cause coolant to enter the combustion chamber.
Engine Block: A crack in the deck of an engine block near a coolant jacket will cause coolant to enter the combustion chamber.
Head Gasket: A damaged or blown head gasket will cause coolant to enter the combustion chamber resulting in white/gray smoke at the tailpipe.