What is a Head Gasket?
We have all heard the term before, but not everyone knows what a head gasket is and what purpose it serves. At the same time, the idea of a blown head gasket induces fear in even the most enthusiastic of gearheads, as the effects of a head gasket failing can be far-reaching. In this discussion, we look at what a head gasket is and how it functions, as well as what the symptoms are when it’s not doing its job anymore.

Firstly, a head gasket forms a seal between the engine block and cylinder head. The engine block contains the crankshaft and pistons, and the engine head contains the valves that let air into the engine, the spark plugs, and the fuel injectors. The camshaft can be block- or head-mounted. An engine head cover with its own gasket goes on top of the cylinder head to cover the valve gear.

There are coolant passages that run through the engine block to the cylinder head, which also pass through the head gasket, with the aim of keeping the engine at the right temperature. The second function of the head gasket is to restrict the coolant flow between the cylinder head and the block, so the openings on the head gasket that line up with the coolant passages are smaller in size. It is also designed to prevent oil and coolant from mixing.

The third function of a head gasket is to account for differences in expansion between the engine block and cylinder head, preventing leaks. In the same way, the gasket mitigates any unevenness on the engine block, preventing leaks between pistons, or leaks to the outside of the engine block.

It has to be strong enough to withstand the forces of the combustion pressure while maintaining a positive seal. If this seal is breached, a head gasket leak develops and we say that the head gasket has “blown”. This could cause the mixing of oil and coolant. If a blown head gasket sounds serious, it’s because it is.

Let’s discuss some of the causes of a blown head gasket, and what signs of a blown head gasket to look out for.

Read more: How To Spot A Blown Head Gasket

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