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Water pump, cooling system

Description
A Water pump is an important part of the engine cooling system. It provides circulation of the engine coolant (antifreeze) through the cooling system (see the top picture).
A water pump moves the coolant through the passages (water jackets) in the engine cylinder block and cylinder head and then out into the radiator. This helps to remove the excessive heat from the engine; the hot coolant passes through the radiator where it cools down and then returns back to the engine.
A water pump is usually driven by the engine through the V-belt or serpentine belt. Sometimes it's driven by a timing belt.
A water pump consists of the housing with the shaft rotating on the bearing pressed inside.
At the outer side there is a pulley mounted on the shaft. At the inner side there is a seal to keep the coolant from leaking out and the impeller that acts like a centrifugal pump (see the lower picture).

Water pump problems
Typical water pump problems include coolant leaks, noisy or defective bearing, damaged or corroded impeller.
Faulty water pump might cause the engine to overheat, which can result in serious engine damage. If defective, a water pump is replaced as a unit.

Is it worth to replace a water pump when a timing belt is being replaced?
Sometimes you might be suggested to replace the water pump at the same time the timing belt is being replaced. In cases when a water pump is driven by a timing belt it's worth to do because it involves very little extra labor, plus, a water pump is subject to wear anyway. As long as the original parts are being used, I'd recommend to go for it.

If you're looking for information how to replace a water pump or other repair information on your car, you can buy an online subscription from Alldata DIY and get an instant access to the repair manual for your car.