Troubleshooting by Exhaust Color
For proper combustion, each combustion chamber requires the correct air-fuel mixture as well as a tight seal. As a result, vehicle emissions and exhaust color can reveal what's going on inside the engine's cylinders.
Blue-gray smoke is an indication of oil burning in the combustion chamber. These are possible symptoms and causes:
Valve Seals: Leaking valve seals 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 allows oil to leak past the gap into the cylinder.
Piston Rings: Worn or damaged piston rings 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 causes excessive crankcase pressure resulting in blue/gray smoke.
Black exhaust smoke is an indication of a rich air-fuel ratio. These are possible causes:
Fuel Injectors: A leaking or dripping fuel injector, causing a rich fuel condition.
Fuel Pressure Regulator: A stuck closed fuel pressure regulator causes a rich fuel condition.
Fuel Return: A restricted fuel return line causes a rich fuel condition.
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) causes coolant to enter the combustion chamber.
Engine Block: A crack in the deck of an engine block near a coolant jacket causes coolant to enter the chamber.
Head Gasket: A damaged or blown head gasket causes coolant to enter the combustion chamber resulting in white/gray exhaust at the tailpipe.