The water pump on your Bmw 3 Series is a key component to keeping your engine cool. Over time the plastic impeller inside can break up resulting in the water not circulating and the engine overheating. The waterpump can be driven off the timing belt and it is a good cost effective idea to change the water pump at the same as the timing belt. If the bearing on the water pump pulley fails it can cause strain on the timing belt which could cause the timing belt to snap leading to high repair bills. orangespanner keep a range of water pumps to suit all budgets.