Thermostat Housing
The metal or plastic cover bolted to the engine that houses the thermostat and connects to the upper radiator hose.
The thermostat housing is a protective cover bolted over the engine thermostat. It acts as the connection point between the engine block or cylinder head and the upper radiator hose, routing hot coolant from the engine back to the radiator.
Typically made of cast aluminum, iron, or molded plastic, the housing seals the thermostat in place with a rubber gasket or O-ring. Because it is subjected to hot coolant, engine vibrations, and high system pressures, it is a common site for cooling system leaks.
Plastic thermostat housings are particularly prone to cracking or warping over time due to thermal stress. A leak at the housing will cause a loss of coolant, leading to engine overheating if not repaired quickly.
Replacing a thermostat housing is a straightforward service. Mechanics scrape the mating surface clean, install a new gasket, insert the thermostat, and torque the housing bolts to specification to ensure a leak-free seal.