The head gasket seals combustion pressure, coolant and oil between the cylinder head and block, all at the same joint. When it fails, the symptoms depend on which of those passages the leak connects. Because several other problems can look similar, it pays to confirm the diagnosis before the head comes off.
Common Symptoms
- Coolant loss with no visible external leak.
- White exhaust smoke with a sweet smell, especially at startup.
- Overheating, or bubbles and pressure in the coolant reservoir.
- Milky or foamy oil on the dipstick or under the oil fill cap.
- Misfire on one cylinder after a cold start, often from coolant entering that cylinder.
- Loss of compression between two adjacent cylinders, causing rough running and low power.
- External leaks of oil or coolant at the head-to-block joint.
How to Confirm It
- Combustion leak (block) test: a chemical tester at the radiator or reservoir neck changes color when exhaust gases are present in the coolant.
- Cooling system pressure test: a pressure drop with no external leak points to an internal leak.
- Compression test: low readings on two neighboring cylinders often indicate a gasket breach between them.
- Cylinder leak-down test: air escaping into the cooling system or an adjacent cylinder pinpoints the leak.
- Spark plug inspection: an unusually clean or steam-cleaned plug can point to the affected cylinder.
Also rule out other causes of the same symptoms, such as a leaking intake manifold gasket, an oil cooler failure or a cracked head or block.
What Causes Head Gaskets to Fail
- Overheating, which can warp the head and crush or damage the gasket.
- Detonation or pre-ignition creating pressure spikes.
- Improper installation: dirty or rough surfaces, wrong torque or sequence, or reused torque-to-yield bolts.
- Neglected coolant that has lost its corrosion protection.
Repair Tips
Find and fix the cause of the failure, not just the gasket. Check the head and block for flatness, prepare the surfaces correctly, use new head bolts where specified and follow the tightening procedure exactly. See our articles on gasket surface preparation and on why torque-to-yield head bolts should not be reused.
Evergreen Head Gaskets and Sets
Every Evergreen gasket is engineered with Eversealed Technologies, matching the sealing material to each engine. Use the Evergreen eCatalog to find head gaskets, head gasket sets and head bolt sets for your application. Browse Evergreen head gaskets and gasket sets.
