Easy guide on how an automotive cooling system thermostat works, this information pertains to most vehicles.
An engine cooling system thermostat is designed to stop the flow of coolant in the cooling system when the engine is cold, this is done to help the engine warm up to optimum operating temperature which improves efficiency and emissions output. Once the engine heats to 195° F or 96° C it will open allowing the radiator to remove heat from the coolant so it can be circulated back into the engine. These units are located either at the upper or lower radiator hose connections.
A housing is used to hold the thermostat in place while allowing the radiator
hose to be connected and keeping the system circulating.
A thermostat is a normal service item that when fails will either stick closed
making the engine overheat quickly, or stick open causing the engine to warm up
to slowly which will trigger a check engine light.
An air bleed is located at the top of the thermostat to allow air to escape from
the system while being filled, a plunger is the actual valve that opens and allows
coolant flow.