How a water pump works
A water pump is vital to a car engine’s operation because it ensures the coolant keeps moving through the engine block, hoses and radiator, and maintains an optimum operating temperature. It is driven by a serpentine belt (aka accessory belt or auxiliary belt) from the crankshaft pulley.
A car’s water pump uses impeller blades and centrifugal force to move the cooled water into the water jacket that sits around the engine’s cylinders, which is where the combustion process take place.
Once the water has flowed around the engine it is taken by hoses to the radiator, usually at the front of the car, where the hot water is cooled by the movement of air over the radiator's fins. It then exits the radiator and flows back into the water pump, where the process starts over.
What happens when a water pump goes bad?
A grinding noise indicates worn water pump bearings. These can sometimes be replaced but it’s easier to get a new pump.
A coolant leak from the water pump could be a sign that the shaft seal or the gasket that sits between the pump and the engine has failed. 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 pump replaced. At the same time, check that all of the hoses are intact and not leaking.
Some modern water pumps have plastic impellers (fan blades) and these sometimes break. This leads to vibrations which in turn cause the pump to fail.
Maintaining a healthy water pump is easy: you need to make sure the engine coolant is in good condition and has the correct amount of antifreeze. The latter stops the water freezing in cold temperatures and acts as a rust inhibitor, preventing small particles from breaking off inside the engine and wearing the pump’s parts.