WATER PUMP IMPELLERa disc with
fanlike blades that spins and produces pressure
WATER PUMP SHAFTsteel shaft that
transfers turning force from the hub to impeller.
WATER PUMP SEALprevents coolant
leakage between pump shaft and pump housing.
WATER PUMP BEARINGplain or ball
bearing that allows the pump shaft to spin freely
in the housing.
WATER PUMP HUBprovides mounting
place for the belt and fan.
WATER PUMP HOUSINGiron 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):
Figure 6-8.Water pump operation.
The spinning crankshaft pulley causes the fan
belt to turn the water pump pulley, pump shaft,
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
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
Fan and Shroud
The cooling system fan pulls a large volume of air
through the radiator core that cools the hot water
circulating through the radiator. A fan belt or an electric
motor drives the fan A fan driven by a fan belt, is
known as an engine-powered fan and is bolted to the
water pump hub and pulley. Sometimes a spacer fits
between the fan and pulley to move the fan closer to the
radiator. Besides removing heat from the coolant in the
radiator, the flow of air created by the fan causes some
direct cooling of the engine itself.
Fan blades are spaced at intervals around the fan
hub to aid in controlling vibration and noise. They are
often curled at the tip to increase their ability to move
air. Except for differences in location around the hub,
most blades have the same pitch and angularity.
Bent fan blades are very common and result in
noise, vibration, and excess wear on the water pump
shaft. You should inspect the fan blades, pulleys, pump
shaft end play, and drive belt at every preventive
A variable pitch (flex) fan has thin, flexible blades
that alter airflow with engine speed (fig. 6-9). These fan
blades are made to change pitch as the speed of the fan
increases so that the fan will not create excessive noise
or draw excessive engine power at highway speeds. At
low speeds, the fan blades remain curved and pull air
through the radiator. At higher speeds, the blades flex
until they are almost straight. This reduces fan action
and saves engine power.
The fluid coupling fan clutch is designed to slip at
high speeds, performing the same function as a flexible
fan. The clutch is filled with silicone-based oil. Fan