Thermostats are temperature-sensitive valves regulating coolant flow between the engine and radiator. Positioned within the engine’s cooling system housing, they maintain optimal operating temperature by restricting coolant circulation until the engine reaches a specified temperature threshold. Operation relies on a heat-responsive actuator – typically a wax pellet – expanding to open or close the valve. Units are specified by opening temperature rating and housing dimensions, crucial for correct system function. Failures commonly present as overheating or inconsistent temperature readings, necessitating replacement to prevent engine damage.