This thermostat assembly regulates coolant flow to maintain the engine within its designed operating temperature range. It is installed in the housing on the engine block, controlling the opening and closing of the coolant circuit based on fluid temperature. A stuck-closed thermostat causes rapid overheating, while a stuck-open unit prevents the engine from reaching proper operating temperature, leading to incomplete combustion and increased wear. The assembly is supplied as a complete unit with the housing, which preserves the correct seal geometry and spring rate for the specific engine application. On reinstallation, clean the mating surface and use a new gasket to prevent coolant leaks.