Knowing the different types of smoke can be helpful to get to the root of the problem and prevent major damage to your car.
White/Grey Smoke
It is important to note that thin white vapour and white smoke are two different signs. While the vapour is a normal occurrence usually due to the condensation build-up from a cold engine, it should go away when the engine has warmed up. White smoke however is a more serious sign, indicating engine problems that need to be attended to immediately!
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 will cause coolant to enter the combustion chamber.
- Engine block: A crack in the deck of an engine block near the coolant jacket will cause coolant to enter the combustion chamber.
- Head gasket: A damaged/blown head gasket will cause coolant to enter the combustion chamber.
Coolant leaks in this respect could result in overheating and major engine damage.
Blue/Grey Smoke
Blue smoke is an indication that oil is being burned in the engine’s combustion chamber due to clogged oil passages or something more serious.
These are possible symptoms and causes:
- Valve seals: Leaking valve seals
- Valve guides: Excessive clearance between the valve stem and the valve guide allows the oil to leak past the gap in the cylinder.
- Piston rings: Worn/damaged piston rings will cause blow-by, resulting in blue smoke.
- Cylinder walls: Worn cylinder walls also cause blow-by, resulting in blue smoke.
- PCV system: A stuck closed PCV valve causes crankcase pressure, resulting in blue smoke.
This could also affect the spark plugs, causing rough idling, resulting in reduced fuel mileage and stunted acceleration.
VAG PRO-TIP: Blue smoke during acceleration means your vehicle’s piston rings may be damaged. During deceleration blue smoke means the cylinder heads’ valve guides are damaged.
Black Smoke
Dark or black smoke usually means the engine is burning too much fuel. A clogged and dirty filter could be the reason. If the filter is clean, these could be possible causes:
- Fuel injectors: A leaking or dripping fuel injector
- Fuel pressure regulator: A stuck closed fuel pressure regulator
- Fuel return: A restricted fuel return line
- Oxygen sensor: A faulty oxygen sensor sending the wrong signal to the engine control module
If your exhaust is sending up smoke signals, play it safe and visit the professionals. Find your nearest VAG Spec Centre and bring your vehicle in for an inspection today!
