Thermostat

The thermostat between the engine's outlet and the radiator opens at a specific temperature, allowing coolant to flow to the air-cooled radiator for cooling. For instance, a valve rated at 195° F begins to open at 195° F and is completely open at around 215° F.

A stuck closed thermostat results in engine overheating because it does not allow coolant to flow to the radiator for cooling. A stuck open thermostat does not allow the engine to reach normal operating temperature, resulting in (TCC) torque converter clutch and air-fuel mixture problems. If a customer mentions that the vehicle sometimes gets hot and suddenly returns to normal, suspect a faulty thermostat. A thermostat that sticks intermittently results in an engine that runs hot and then suddenly cools, returning to normal operating temperature when the valve opens.