White smoke from exhaust
Dense white (or bluish) smoke, especially after warm-up — a sign of coolant or water entering the combustion chamber.
A little white vapour on a cold start in cold weather is normal (condensate in the exhaust). Real white smoke is thick, doesn't clear after warm-up, and may smell sweet (coolant).
Most alarming cause: blown or cracked head gasket. Coolant enters the combustion chamber, burns — hence white vapour. Also: cracked block or head, failed EGR cooler valve (diesel).
OBD-II signs: rich mixture (negative LTFT), P0217 (overtemp), long-duration misfires. Some vehicles show a "Fuel Dilution" code when coolant gets in the oil. Main clue: coolant level dropping with no visible external leak.
First diagnostic steps
- Check coolant level (dropping without external leak = suspect head gasket)
- Check oil on dipstick for milky colour or foam (coolant in oil)
- Look for bubbles in the expansion tank with the engine running
- Do a combustion gas / CO2 test on the cooling system (CO2 test kit)
- Measure compression in all cylinders
Likely fault codes
Click a code for detailed description, causes, and diagnostic plan.