Head gasket leak signs

Symptoms

• White smoke from the exhaust that doesn't clear quickly
• Milky or frothy oil on the dipstick
• Bubbles in the coolant reservoir while the engine runs
• Overheating with no obvious external leak, or a sweet smell from the exhaust

Likely causes

• CommonGasket failure between two cylinders or a cylinder and a coolant passageThis lets combustion gases, oil, and coolant cross-contaminate depending on exactly which passages are affected.
• CommonPrevious overheating event weakening the gasketA past overheating incident, even one that seemed resolved, can leave the gasket compromised and prone to later failure.
• PossibleWarped cylinder head from overheatingHeat can warp the head enough that even a new gasket won't seal properly until the head is resurfaced or replaced.
• PossibleOriginal gasket simply reaching end of lifeOn some engines, head gaskets are known to fail around certain mileages regardless of maintenance.

What to do

1. Check for any combination of white exhaust smoke, milky oil, or bubbles in the coolant reservoir with the engine running and the cap off (carefully, only when cool).
2. Check the coolant level for unexplained drops with no visible exterior leak.
3. Avoid continuing to drive if more than one of these signs is present, since combined symptoms strongly suggest gasket failure.
4. Have a mechanic run a chemical combustion leak test on the coolant, which is the standard way to confirm a head gasket issue.
5. Ask about checking the head for warping if a leak is confirmed, since resurfacing may be needed alongside gasket replacement.
6. Plan for the vehicle to be out of service for a meaningful repair, since head gasket jobs typically take a day or more.
7. Address the root cause (like an overheating event) alongside the gasket repair to avoid a repeat failure.

Tools and parts

When to call a pro

See a mechanic for a combustion leak test to confirm the diagnosis before committing to a major repair.

Safety