The head gasket is fitted between the cylinder head and the engine block. Its function is to provide a gas and watertight seal to ensure that engine compression is maintained and to prevent leakage of oil or coolant into the combustion chambers. The gaskets used on modern cars are made up from multiple layers of steel (MLS), which are covered with a rubber coating, which adheres to the engine block and cylinder head surfaces. Some gaskets are made from a Solid Copper sheet, which incorporate raised copper 'o' rings. Another type of gasket that has been used is the Elastomeric gasket, which uses a bead of silicone to provide the seal, this type of gasket was fitted to the Rover K-series engines and proved to be unreliable and replacement gaskets are now of the MLS type.
1 Coolant can leak into the cylinders, which will cause the engine to overheat rapidly, and heavy white smoke will be emitted from the exhaust system. Coolant can then mix with the engine oil forming a creamy sludge, which has limited lubricating properties. Prolonged use of an engine with this type of fault can result engine failure.
2 Coolant can leak from the gasket to the outside of the engine block, this is usually due to a crack in the gasket surrounding a water jacket.
3 Compression can be reduced or lost if the gasket fails between two cylinders, which will result in a significant loss of power.
4 Oil can leak externally from a small crack in the head gasket that surround an oil gallery.
5 Coolant can mix with the engine oil if a crack in the gasket occurs between a water jacket and an oil gallery. The oil and coolant mix forms a creamy sludge, which has limited lubricating properties. Continued use will damage the crankshaft bearings.
6 Compression can enter the cooling system, which will cause the system rapidly overheat and pressurise.
Gaskets can fail as a result of wear and tear from extreme temperature variation but typically gasket fail due to the engine overheating. Over heating engines are a common issue and are usually caused by:
1 A leaking cooling system from the radiator, a hose or the water pump.
2 A faulty thermostat that does not open at the correct time
3 A faulty pressure cap that does not hold pressure in the cooling system
4 A water pump impellor that is adrift front its spindle