Head gasket failures cause excessive overheating that can severely damage engine components, significant loss of engine power, abnormal fuel combustion and oil and coolant mixing that could lead to engine block cracking. The main purpose of a head gasket is to keep engine compression and separate coolant and oil circulation.
Head gaskets are made of multiple layers of steel coated with a rubber-like substance that stands up to high temperatures generated by the engine's combustion chamber. Without the efficient sealing effect of a head gasket to restrict coolant and oil from mixing, water can enter the engine's combustion chamber, causing engine hydrolocking and engine block cracking. A car with a blown head gasket may be driven for some time, but its major engine components will succumb to overheating and bad fuel combustion and eventually permanent damage.
According to How Stuff Works, head gasket failures are very easy to diagnose. The common symptoms include constant overheating, low oil and coolant levels and white smoke mixed with water coming out of the exhaust pipe.
Head gaskets are seated between the cylinder head and the engine block, and replacing them can be difficult because a mechanic needs to remove large engine components, according to Cars Direct.