Q:

What causes a blown head gasket?

A:

Quick Answer

Engine overheating is the number one cause of head gasket failures, according to Mobil Oil. The cylinder head and engine block expands beyond acceptable limits while overheating, which leads to head gasket pinching. Improperly torqued head bolts and abnormal air fuel mixture combustion are common reasons as well.

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Full Answer

Head gaskets are made of compressed multiple layers of steel that are held together by a rubber-like coating that acts as a sealant between the engine block and cylinder head. Most modern cylinder heads are made of aluminum, which has a higher thermal expansion rate than steel and iron. Excessive overheating causes the cylinder head to expand and crush the head gasket into failure.

The main function of a head gasket is to hold engine compression while keeping oil and coolant circulation separate. Undetected blown head gaskets cause coolant and oil mixing, which could lead to severe engine damage, such as engine block cracking.

According to HowStuffWorks, head gasket failures are fairly 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.

The head gasket is seated between the cylinder head and the engine block, and replacing it can be difficult because a mechanic needs to remove a large set of engine components, according to Cars Direct.

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