Amazingly, up to a third of the heat energy produced inside an engine's combustion chambers ends up as waste heat that goes into the block. This heat must be eliminated, otherwise the engine will overheat and self-destruct.

The water pump keeps coolant circulating between the engine and radiator to get rid of the heat. The pump is usually belt-driven and turns continuously while the engine is running. Most pumps are mounted on the front of the engine and are driven by a V- or serpentine belt. Some water pumps are mounted under the timing belt cover on OHC engines and are driven by the timing belt. A few are mounted on the back of the engine or head and are driven by the camshaft.

The water pump housing itself is usually made of cast iron, aluminum or stamped steel. Inside the housing is a paddle-style impeller mounted on a shaft supported by a bearing and seal assembly. The bearing assembly has two sets of bearings (ball or needle style) with a seal to prevent coolant from leaking out of the pump. The back of the pump housing may have a cover or bolt directly to the block, requiring a separate gasket.

Pump Function
On most engines, the pump pulls coolant in through the lower radiator hose and pushes it into the block. The coolant then flows up through the heads and returns to the radiator through the thermostat housing and upper radiator hose. On some vehicles, a "reverse flow" system is used. In this style of sy...