Vital to proper engine function, thermostats regulate the flow of coolant between vehicle engine and radiator. These misunderstood, but seemingly simple devices can typically be found in an accessible location near the top of the engine, and should be repaired or replaced immediately if found to be malfunctioning.
Function
The thermostat has two primary functions in an any engine. On start-up -- especially under cold conditions -- the thermostat closes the radiator off from the cooling system, allowing the engine to warm up to operating temperature more quickly. The engine also relies on the thermostat to maintain engine temperature during cruising -- usually around 192 to 195 degrees Fahrenheit in modern cars -- by regulating the flow of coolant to the radiator to maximize fuel efficiency.
Design
Thermostats are relatively simple as engine parts go, and function as cooling system valves that operate mechanically, based on the temperature of the engine coolant. As the temperature increases, the wax inside the thermostat expands, pushing a spring-dampened piston downward, opening the valve and allowing coolant to enter the radiator, where it can be cooled before re-entering the engine. Under cold starts, the valve remains shut, allowing the coolant to continually circulate through the engine and warm up more quickly.
Replacement
Non-functioning thermostats require immediate attention, because engine over-heating due to a stuck thermostat could leave you stranded on the road. Luckily, these small devices can be bought relatively inexpensively, and are typically attached with just two bolts and a gasket or rubber seal.
