If you’ve wondered how much work a water pump must do, remember that only about 30% of the heat energy produced by combustion results in mechanical energy. That estimate, of course, is a mathematical comparison between the heat value of the gasoline going into the engine, and the heat value of the mechanical energy coming out of the engine. The remainder of combustion heat must then be dissipated into the atmosphere through the exhaust, lubrication and cooling systems.

Water pump operation is important because, if the coolant’s circulation rate is too slow, the coolant will begin to boil in the engine’s water jackets. Unfortunately, when coolant boils, it becomes gaseous and can no longer cool hot cylinder walls and cylinder heads. The result is overheating, which is a primary cause of catastrophic engine failure.

To prevent the coolant from overheating, a water pump is used to circulate the coolant through the engine’s cylinder block, heads and radiator. As it circulates, the coolant absorbs heat from the engine block and dissipates it into the atmosphere through the radiator.

Of course, coolant temperatures may vary according to ambient temperature, engine load and engine speed. Most modern engines must operate between 185