Why is white smoke coming from my exhaust?

Thin white smoke on a cold morning is just water vapor — normal and goes away once the engine warms up. Thick, persistent white smoke that smells sweet is coolant burning, which usually means a blown head gasket, cracked head, or failed intake manifold gasket.

Cost range: $200–$3,000. Severity: high. Safe to drive? Persistent white smoke: stop driving. A blown head gasket can mix coolant into the oil and seize the engine.

Most likely causes

1. Normal water vapor (cold start) — Disappears within 1–2 minutes as the exhaust warms up. No action needed. ($0, common)
2. Blown head gasket — Sweet-smelling thick white smoke, milky oil on the dipstick, bubbling in the coolant reservoir, or coolant loss with no leak. ($1,500–$3,000, common)
3. Cracked or warped cylinder head — Often the result of severe overheating. Symptoms similar to a head gasket but worse. ($1,500–$3,500, less common)
4. Failed intake manifold gasket — On engines with coolant passages through the intake (common on older GM 3.4/3.8). Cheaper than a head gasket. ($200–$700, less common)