A small puff of white smoke from the exhaust on a cold morning is usually just condensation burning off - completely normal. But thick white smoke that does not clear after a minute, or a sweet smell with the smoke, is a coolant problem and can mean a head gasket.
A small puff that clears in 30 seconds on a cold morning is harmless. Thick, persistent, sweet-smelling white smoke is coolant in the cylinders - stop driving and get it diagnosed. Driving with a blown head gasket can crack the head and double the repair cost.
Water vapor is a normal byproduct of combustion. On cold mornings, that vapor condenses inside the cool exhaust and puffs out as white steam at startup. It clears within 30-60 seconds and has no smell. Nothing to worry about.
Get a free vehicle-specific diagnosis →If white smoke is thick, persistent, and sweet-smelling, coolant is leaking into the combustion chamber. You will also lose coolant from the reservoir without seeing leaks, and may see milky residue on the oil cap. This is serious.
View Full Diagnosis - P0301 →A crack in the head or block lets coolant into the cylinder. Symptoms look identical to a blown head gasket. Often the result of severe overheating or an unrepaired head gasket leak.
Get a free vehicle-specific diagnosis →Some engines route coolant through the intake manifold. A crack there leaks coolant directly into the intake, where it gets sucked into the cylinders and burned as white smoke. Common on certain GM 3.1L and 3.4L engines.
Get a free vehicle-specific diagnosis →Is the white smoke harmless condensation or a $3,000 head gasket warning? Tell us your symptoms and we will tell you which.
Get a free vehicle-specific diagnosis →Takes under a minute. Tell us your year/make/model and what you're seeing.
These codes are commonly thrown alongside white smoke caused by coolant entering the cylinders.
A small puff that clears within 30-60 seconds on a cold morning is normal water vapor from combustion. Thick, persistent smoke - especially with a sweet smell - is not normal and points to coolant in the cylinders.
Three checks: time (condensation clears in under a minute), smell (condensation has no smell, coolant is sweet), and coolant level (condensation does not lower the reservoir, head gasket leaks do).
If it is condensation, drive freely. If it is coolant (sweet smell, persistent, dropping reservoir), stop driving and get it towed for diagnosis. Driving with coolant in the cylinders can warp the head and turn a $1,500 fix into a $4,000 fix.
A head gasket job runs $1,500-$3,000 on most cars. If the head is warped or cracked from driving overheated, the head needs to be machined ($200-$400) or replaced ($800-$2,000). Catch it early to keep the cost down.