Which component circulates coolant through the engine cooling system?

• A. Water pump
• B. Radiator cap
• C. Thermostat
• D. Radiator fan

Answer: (A)

Circulating coolant through the engine cooling system is the job of the water pump. The pump uses an impeller to push coolant from the radiator into the engine’s cooling passages and back again, creating a continuous loop that carries heat away from the engine. It is typically driven by the engine’s belt and must function for effective cooling; if it fails, overheating ensues because the coolant stops moving.

The radiator cap, while important for maintaining system pressure and sealing the reservoir, does not move coolant. The thermostat acts as a temperature-controlled valve that opens or closes the path between the engine and radiator, regulating when coolant flow occurs. The radiator fan helps dissipate heat by moving air through the radiator but does not circulate the coolant itself.