Usually by overheating, which can be caused by a blown head gasket, cracked head or a leaking block. Bar?s Leaks head gasket repair eliminates this problem ? guaranteed. This product contains a blend of Aramid and refractory fibers, which provide the strength of a bulletproof vest and the heat resistance of fireproof clothing. As these particles penetrate a crack or the blown head gasket area, they lock together and bond, forming a hard, permanent ceramic-type seal.