Engine operating temperature is regulated by the

• A. Thermostat
• B. Water pump
• C. Radiator cap
• D. Oil cooler

Answer: (A)

The thermostat is the device that regulates engine temperature by controlling coolant flow. When the engine is cold, it stays closed to restrict coolant from circulating through the radiator, allowing the engine to warm up quickly. Once the coolant reaches its set temperature, the thermostat opens gradually, letting hot coolant flow to the radiator to be cooled by air and keep the engine at its optimum operating temperature. The water pump merely moves coolant through the system; it doesn’t regulate temperature by itself. The radiator cap controls system pressure, which raises the coolant’s boiling point but doesn’t regulate temperature. An oil cooler affects the temperature of the engine oil, not the engine’s coolant temperature.