White Smoke: Normal Vapour or Burning Coolant?
On a cold or damp morning, a thin wisp of white smoke that clears within a few minutes is simply condensation — nothing to worry about. What should concern you is thick, persistent white smoke from a warm engine with a faintly sweet smell: that is coolant burning inside the cylinders.
Likely Causes
- Failed head gasket. It allows coolant to leak into the combustion chamber. This is the most common cause.
- Cracked cylinder head, often following overheating — particularly common on diesel engines.
- Damaged oil/water heat exchanger: oil and coolant mix together.
- On a diesel, a faulty injector or glow plugs can produce a white-grey smoke from poorly burnt fuel, especially when the engine is cold.
Can You Keep Driving?
As little as possible, keeping a close eye on the temperature gauge. A leaking head gasket causes the engine to overheat, and overheating warps the cylinder head — making the repair far more costly. If the needle approaches the red, pull over immediately.
Repair or Replace?
A head gasket can be replaced provided the engine has not overheated too severely, but this must always be accompanied by an inspection and skim of the cylinder head. If the head is cracked or the engine has overheated badly, a reconditioned engine on an exchange basis, supplied as a bare engine, is often the safer option: you keep your ancillaries and benefit from a warranty of up to 24 months. Before fitting, make sure the cooling system is checked thoroughly.
