Smoke and smells
White smoke from the exhaust: what it means and what to do
A little white vapor on a cold start or in damp weather is condensation and clears within minutes. If the white smoke is thick, carries on with a warm engine or smells sweet, coolant may be burning; on a diesel it can also be unburnt fuel.
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Reviewed by Daniel Morales, founder of Reprorace SL, on
Is it serious? Can I keep driving?
Carefully, and only as far as the garage. If it is only vapor that clears as the engine warms, it is not a fault. If it is thick and constant, watch the temperature gauge or light and get to a garage soon; if the temperature rises or the coolant level drops, stop as soon as it is safe.
A careful, general answer: only someone who inspects the car can say whether it is safe to drive. When in doubt, stop somewhere safe and call for assistance.
Most likely causes
- Condensation: normal when cold and damp; it clears once the exhaust is hot.
- Coolant in the combustion: head gasket, a cracked head or a leaking EGR cooler; the smoke smells sweet and the level drops.
- Unburnt fuel on a diesel: glow plugs, injectors or a hard cold start give white-gray smoke with a strong diesel smell.
- Particulate filter regeneration: some diesels show a little white vapor while regenerating.
Listed from more to less common in general; on your car they may be different. A fault-code reading and a check at the garage confirm which one it is.
To understand it better: What does the engine thermostat do and what does P0128 mean? What is EGR and what happens when it fails?
Car system: Cooling
What you can check yourself
See whether it clears after a few minutes of driving or carries on with the engine warm.
With the engine cold, check the coolant reservoir level and check it again a few days later.
Smell the smoke from a safe distance: sweet points to coolant; diesel points to incomplete combustion.
Watch the temperature gauge or light while you drive.
Safe checks only: with the engine off and cold whenever you look under the hood, without taking anything apart and without touching hot or moving parts.
Related fault codes
- P0217Engine coolant: over temperature
- P0128Coolant thermostat: coolant temperature below the thermostat regulating temperature
- P0380Glow plug/heater, circuit A: malfunction
- P0671Cylinder 1 glow plug, circuit open
- P0401EGR A flow: insufficient flow detected
Generic codes that often come with this symptom. Seeing one does not confirm the cause: it is where the diagnosis starts.
How the ECO-LITE helps diagnose it
Plugged into the OBD socket, the ECO-LITE reads the fault codes of the control units that answer, with the freeze-frame data captured when the fault happened, and shows live data on your phone or computer. With your permission, your garage can see them remotely before you bring the car in.
What to look at here: coolant temperature, glow plug and preheating status on diesels, and misfires.
Frequently asked questions
Is white smoke normal on a cold morning?
Yes, if it is thin vapor that clears as the engine warms, especially in winter or damp weather.
How do I know if it is the head gasket?
Typical signs: thick, constant white smoke with a sweet smell, coolant disappearing with no visible leak and a rising temperature. The garage confirms it with pressure tests or a test for exhaust gas in the coolant.
Can I keep driving with white smoke?
If it is condensation, yes. If it is thick and persistent, only to the garage while watching the temperature: an engine without coolant is damaged very quickly.
Keep reading
- Engine cooling: how it works and what fails
- Engine temperature warning light on: what to do
- Glow plug light on or flashing: what to do
- Blue smoke from the exhaust: the engine is burning oil
- Car symptoms: what they mean and what to do
- Check engine light on: what to do
- How to read and clear your car's fault codes
- OBD fault codes: what each one means