The car water pump is a throwback to motoring's early days when engines were cooled by water alone, unlike today's vehicles that use a mixture of water and antifreeze. What hasn't changed is the car water pump's importance in preventing the engine from overheating, making it a crucial component of a vehicle's cooling system. Here's how it works and why replacing it could be a money-saver.


Whenever internal combustion engines are running, they're generating heat with temperatures under the bonnet soaring to more than 200 degrees. Once an engine reaches optimal operating temperature, that excess heat has to be removed to prevent the buildup of high temperatures that will cause engine damage. This is where the car water pump comes in. It sucks antifreeze from the radiator and circulates it through and around the engine. That engine heat is transferred from the engine block to the antifreeze, which then flows back to the radiator where it's cooled, and the process begins anew.

On most vehicles, the car water pump is driven by the engine's serpentine belt, which is connected to the pump's pulley. The pulley and belt work together to move coolant through these steps:

  1. Coolant is sucked in at the centre of the impeller
  2. Centrifugal force pushes it out through the impeller blades
  3. It then goes through a scroll, which directs the coolant flow into the engine without reducing its velocity

Most car water pumps also have a weep hole that allows a small amount of coolant to seep out of them. However, if you see a constant flow of coolant from the hole, it means the seal has failed and the pump needs to be replaced. Some vehicles also use an electric car water pump that is powered by an electric motor instead of the serpentine belt.

Water Pump Impeller


The only downside with water pumps is that they don't last forever and need to be replaced periodically. The pump's numerous gaskets and seals can become brittle with age and can crack, or the pulley's bearings can go bad, both of which lead to failure.

When a water pump does fail, it's a major problem because it means coolant is no longer adequately circulating, temperatures are rising and overheating is soon to follow. Fortunately, water pumps often provide some warning that they're going to fail. Here are some clues to be on the lookout for:

  • Coolant leaking onto the ground. This is probably the easiest one to spot. Any coolant leak is cause for concern, but when it's related to the water pump, the leak will appear on the ground near either the front of the centre of the engine and the liquid will be either green, orange/red or possibly blue colour. Don't mistake the water you see dripping under the car on a hot summer's day while the vehicle's A/C is running with a coolant leak. This water is a normal byproduct of the A/C system and won't be coloured like antifreeze is. Even if you don't see coolant leaking onto the ground, if you're having to add coolant regularly, it means there is a leak somewhere in the system. Try using a cooling system pressure tester to pinpoint the leak.
  • Low coolant warning light. If your vehicle is losing coolant, regardless of how fast or slow it's happening — it's a warning sign that there could be a water pump problem. The leak needs to be diagnosed to determine where in the cooling system it's occurring.
  • Temperature warning gauge. If the engine temperature gauge or the temperature light show that the engine is running hotter than it should be, that's another sign that there's a cooling system problem caused by the water pump.
  • Grinding or high-pitched whining noise. These types of noises coming from the engine compartment, particularly if they increase in tandem with engine RPMs, could indicate that the serpentine belt is too loose on the water pump pulley or that the pulley's bearings are going bad.

Water Pump Pulley


As soon as a car water pump shows signs of failure, it needs to be replaced. And, because of the pump's location under or behind the timing belt cover, most vehicle manufacturer specifications and auto technicians recommend replacing the water pump at the same time the timing belt is replaced even if the pump isn't exhibiting any signs of failure. That's partly because of the time, effort and expense associated with replacing a timing belt. You don't want to do that job and not replace the water pump, only to have the water pump fail a few months later and have to go back in and repeat most of the same work.

For all its importance in protecting the engine from damage, a car water pump isn't a super expensive part, usually costing around £100 to £150, which is all the more reason to replace it at the first sign of trouble.