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What is a Thermostat Housing?

By Jeremy Laukkonen
Updated Feb 28, 2024
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In many engines, the thermostat housing serves as the coolant outlet and is located on either the cylinder block or intake manifold. Coolant typically flows out of the housing, through a large hose, and into the radiator. These housings hold the thermostat that regulates the flow of coolant through the engine and radiator. They are typically made of a plastic composite, aluminum, pot metal, or other similar materials. A fiber gasket will typically be used to connect the thermostat housing to the block or intake manifold, though plastic and rubber gaskets also exist.

The main purpose of a thermostat housing is to contain the engine thermostat and provide a coolant outlet to the radiator. In some cases, each radiator hose will be connected to a similar looking housing, with one serving as a coolant inlet and the other as an outlet. The thermostat housing will typically be the one with a larger bulge where it meets the engine, as it has to have room for a thermostat while the other, empty housing is simply an inlet or outlet point.

In addition to holding the thermostat, these housings may also serve as an air bleed point for the cooling system. A thermostat housing may have a bleed valve that can be loosened to allow the escape of any air that has been trapped in the block. Not every vehicle has this feature, though it can be very useful any time the cooling system is drained and refilled, or flushed out.

When a thermostat is suspected of failure and needs to be inspected or replaced, the housing must be removed. This is typically a simple operation, though some vehicles have thermostat housings that are very difficult or time consuming to reach. The best way to locate the thermostat is typically to follow each radiator hose to the engine and determine which connects to a removable housing. If both hoses connect to a removable component, there will typically only be one that appears capable of containing a thermostat.

In some cases, a thermostat housing may begin leaking and require replacement. Another reason for replacement is if pitting develops on the gasket surface, which may be noticed when the housing is removed to service the thermostat. As coolant breaks down over time it can become acidic and eat away at things like gaskets and hoses, though it may also attack metal, such as the internal components of the water pump or the mounting surface of a thermostat housing. When this happens, the housing typically has to be replaced.

WikiMotors is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.

Discussion Comments

By Rundocuri — On Jan 28, 2015

@ocelot60- When your nephew starts automobile repair school, he will learn all about automobiles and how they operate. Since he will need to knowledge so he can fix all kinds of issues, learning about auto parts such as the thermostat housing will be the foundation of his coursework.

By Ocelot60 — On Jan 27, 2015

I have a nephew who is planning to go into automobile mechanics because he would like to own a auto repair garage some day. Is a concept like thermostat housing something that he should expect to learn about in auto mechanics school?

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