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How do the gaskets in the engine protect it and keep it working?
Gaskets in an engine are used to seal one part to another due to variations from the machining or casting process. When a part is made, the surface will not be perfectly flat. There are small machining lines and surface imperfections that if two parts were put together, they would not be able to stop leakage of fluids. There may also be two different materials or thicknesses that will cause the two parts to expand and contract at different rates. The two parts would not be able to seal without the use of a seal or gasket.
There are many different gaskets used in an automotive engine. There are gaskets between the engine block and cylinder head. These gaskets may have layers of metal and different gasket materials to seal in the compression of the cylinder. The same gasket is used to seal oil and coolant passages from leaking. The gasket material will take up any imperfections between the two parts and any expansion or contraction of the parts as they get hot and cool back down. You may have a plastic part being sealed to a metal part or an aluminum part to a steel part.
The gasket material will be specific for the application. There are paper, plastic, metal, rubber or neoprene and silicone types. There are also gaskets made with combinations of these materials. The different materials are used to withstand the pressures of fluids or combustion. For example, you may see metal or paper gaskets on cylinder heads. Rubber or silicone gaskets are commonly used on valve covers and oil pans.
A gasket is only good as a one time use in most cases, except now some oil pan or valve cover gaskets are reusable and made from metal or plastic with different types of rubber or neoprene bonded to the metal or plastic. These type of gaskets use special shoulder bolts that cannot be overtightened in case they crush the gasket. Silicone can be used in place of a gasket and is called “Form-A-Gasket” by the manufacturer. The silicone is used in low pressure applications and works well when hardened to seal out coolant or oils. Water pump, oil pans, and thermostats use silicone on some applications.
Gaskets are designed to seal two parts in normal operations and will have a tolerance in temperature, pressures, or fluids that it can withstand. When these things go below or above and beyond the specified operating limits of the gasket, they can fail. When a gasket is new it may be able to withstand some operations out of these limits but an older gasket may not be able to. When a gasket fails there may be warping between the two parts and replacing the gasket may not be enough to seal the two parts again. For instance, if a head gasket starts leaking due to engine overheating](https://www.yourmechanic.com/services/car-is-overheating-inspection), the heat may warp the surface of the cylinder head to the point that a new gasket would not be able to seal again unless the head surface is machined flat again.
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