Head Gasket

It has to seal combustion pressure in each cylinder while also sealing the coolant and oil passages that cross the joint. Modern gaskets are usually multi-layer steel. Overheating is the most common cause of failure: the head can distort and the gasket can no longer seal. Failure can let coolant into the cylinders or oil, or combustion gas into the cooling system.

Modern head gaskets are usually multi-layer steel (MLS). They must handle high combustion pressures and temperatures while sealing oil and coolant channels between head and block.

Head bolts clamp the gasket between head and block with high force. The layers and embossed beads seal around each opening. The cylinder head bolts press the head onto the gasket with a precise torque. Many engines use stretch bolts that must be replaced whenever the head is removed.

Signs include white smoke, loss of coolant without visible leaks, bubbles in the expansion tank, overheating and misfires. A workshop confirms it with a chemical test for exhaust gas in the coolant and a pressure test. Typical signs of a blown head gasket are coolant loss, white smoke, overheating, bubbles in the expansion tank and milky oil. Continuing to drive can warp the head and cause much more damage.