Water Pump

The water pump is an impeller or centrifugal pump that forces coolant through the engine block, cylinder head, intake manifold, hoses, and radiator (fig. 6-7). It is driven by a fan belt running off the crankshaft pulley.

The major parts of a typical water pump include the following:

• WATER PUMP IMPELLER—a disc with fanlike blades that spins and produces pressure and flow.
• WATER PUMP SHAFT—steel shaft that transfers turning force from the hub to impeller.
• WATER PUMP SEAL—prevents coolant leakage between pump shaft and pump housing.
• WATER PUMP BEARING—plain or ball bearing that allows the pump shaft to spin freely in the housing.
• WATER PUMP HUB—provides mounting place for the belt and fan.
• WATER PUMP HOUSING—iron or aluminum casting that forms the main body of the pump.

The water pump normally mounts on the front of the engine. With some transverse (sideways) mounted engines, it may bolt to the side of the engine and extend towards the front.

A water pump gasket fits between the engine and the pump housing to prevent coolant leakage. RTV sealer may be used instead of a gasket.

Operation of the water pump is as follows (fig. 6-8):

• The spinning crankshaft pulley causes the fan belt to turn the water pump pulley, pump shaft, and impeller.
• Coolant trapped between the impeller blades is thrown outward, producing suction in the central area of the pump housing.
• Since the pump inlet is near the center, coolant is pulled out of the radiator, through the lower radiator hose.
• After being thrown outward and pressurized, the coolant flows into the engine. It circulates through the block, around the cylinders, up through the cylinder heads, and back into the radiator.

Figure 6-7.—Water pump.

Figure 6-8.—Water pump operation.