A
head gasket is something used in an
internal combustion engine to create a seal between the
head(s) (containing the
valves and (usually) the
camshafts) and the
engine block (containing the
pistons and the
crankshaft). The head gasket performs several functions. It aids in creating a close to near-perfect
seal in the
combustion chamber formed in the space where the head and cylinders meet, so that there is no
leakage from the engine in the
combustion process. The gasket also acts to seal the interconnecting
coolant passages that flow through the head and the block, so that none of the coolant will leak into the combustion chamber or the top of the head where the valves or cams are.
Head gaskets are prone to rupture (or "blowing") due to excessive combustion chamber pressure (i.e. from aftermarket turbocharging systems), or from extreme engine temperature (coolant becoming too hot and boiling, sometimes explosively).