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How a car water pump works

Car water pump guide

What does a car water pump do?

A car water pump moves the coolant through the engine block, radiator and hoses, and ensures an optimum operating temperature is maintained. The water pump is usually powered by an auxiliary drive belt (aka serpentine belt or accessory belt) but can also be driven by the timing belt (see below).

The water pump uses impeller blades and centrifugal force to move the cooled water into the car’s engine, or rather the water jacket that sits around the engine’s cylinders, which is where the combustion processes take place.

Once the coolant has flowed around the engine it is taken by hoses to the radiator, usually at the front of the car, where the water is cooled by the movement of air over the radiator's fins. It then leaves the radiator and flows back into the car water pump, where the process starts over.

Water pump car

Is my car water pump broken?

The most common problem with water pumps is worn bearings. The biggest clue of worn bearings is a grinding or a rumbling noise; it may be possible to replace the bearings and the seals, but for peace of mind, the complete water pump is normally replaced; they’re not that expensive.

Other water pump problems include coolant leaks. These tend to be caused by a failed shaft seal or the gasket that sits between the pump and the engine. If it’s the shaft seal the entire pump will need to be replaced, but if it’s the gasket the pump can be removed, a new gasket fitted and the original water pump replaced.

Some modern cr water pumps have plastic impellers (fan blades) and these sometimes break. This leads to vibrations which in turn cause the pump to fail. It’s also possible for the impeller to become loose on the shaft, so although the impeller looks OK, it doesn’t pump anything.

Timing belt

How long does a car water pump last?

Your car's water pump is always running when the engine is on, so you can't really go by the number of kilometers on the odometer when trying to work out how much life is left in your pump. 

If your car's water pump is driven by the timing belt, the belt must be renewed at the same time as the pump. In fact, some manufacturers recommend the pump is renewed whenever the belt is replaced. That's because a water pump can seize when it goes wrong - that's a simple replacement job if it's powered by an aux belt, but it could cause big issues if it's timing belt-driven because it can cause the belt to lose teeth and throw the engine's timing out of kilter. So it's important to renew the timing belt and pump at the same time, to reduce the likelihood of that happening.  

Maintaining a healthy water pump is easy: you need to make sure the engine coolant is in good condition and has the correct specification and amount of antifreeze. The latter stops the water freezing in colder parts of the country, and acts as a rust inhibitor wherever you live, preventing small particles from breaking off inside the engine and wearing the pump’s parts. So always use antifreeze, even if you live in Darwin!