leak-down test or a chemical test that identifies hydrocarbons in the coolant fluid. The cost of the replacement component (i.e. the head gasket itself) is usually relatively low, however there are significant labor costs involved in the replacement process. This is because the process of removing and replacing the cylinder head is a time-consuming task. Effect of engine knocking Engine knocking (detonation) can be caused by poor quality fuel, an engine fault or if inappropriate fuel and/or ignition settings are trialled chosen while engine tuning is taking place. If the detonation is severe, the cylinder pressure can be increase to eight times above normal pressures, which can cause the cylinder head to lift away from the engine block, disrupting the seal between the two. Most gaskets used in standard production engines can be critically damaged by severe detonation. See also Internal combustion engine cooling Motor oil Rocker cover gasket References Seals (mechanical) Engine technology Engine problems