This thermostat regulates the coolant flow in the engine cooling circuit, maintaining the operating temperature within the designed range. It opens at a calibrated temperature to allow coolant to pass through the radiator, and closes when the engine is cold to speed warm-up. A failed thermostat stuck in the open position prevents the engine from reaching proper operating temperature, while one stuck closed causes overheating. This component is manufactured to the original spring-rate and opening-temperature specifications, ensuring the engine management system receives the correct coolant temperature signal for fuel metering and emissions control.