What Causes a Cracked Head Gasket?

Written by dennis hartman
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What Causes a Cracked Head Gasket?
An engine needs secure head gaskets to operate properly. (American v8 engine image by kenmo from Fotolia.com)

Gasoline-powered cars and trucks are propelled by an internal combustion engine. The head gasket is a plate that helps to seal off the different parts of the engine, including the individual combustion chambers. Head gaskets are usually made from steel or another metal alloy. When they crack, or "blow," they may allow engine coolant to mix with fuel, causing a number of major engine problems.

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The most common cause of a cracked head gasket is engine overheating. As the engine reaches unsafe operating temperatures of several hundred degrees, the steel gasket can crack, opening the sealed-off cylinders and allowing engine coolant to leak into the combustion chambers, depending on the location of the crack.

Engine overheating has many different causes including a leak in the coolant tank, radiator or one of several hoses. Engines can also overheat when the fuel pump fails, if a blockage prevents the radiator from accessing cool air, or if the thermostat fails and prevents the engine fan from kicking in to cool off the engine.

Early Ignition

Improper engine timing can change the compression in each combustion chamber, causing a crack in the head gasket. This can happen if one or more spark plugs fails to fire at the right moment due to a malfunction or misalignment. An engine can also experience early ignition with the wrong type of fuel is used. Also, if one or more valves fail to close on time during the engine's cycle of intake, compression, ignition and exhaust it can't lead to early ignition.

Improper Assembly

An engine with any of its major components installed incorrectly is more susceptible to a cracked head gasket. Placing the gasket in the wrong position or failing to bolt it onto the engine block may allow it to shift position under the intense pressure it is meant to endure. Improper assembly of the spark plugs, valves or other engine components can cause early ignition or overheating and lead to a cracked head gasket too.


Though uncommon, some head gaskets can crack simply due to wear and tear over time. The head gasket experiences strong pressure every time the engine runs, as well as extreme temperature fluctuations during cold weather. Low quality head gaskets are most susceptible to cracking due to age.

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