Water Pump
Water pumps come in many designs, but most include a rotating impeller, which forces the coolant through the engine block. In most rear wheel drive cars, the fan is installed on the end of the water pump shaft. Many water pumps have a springloaded seal to avoid leakage of water around the pump shaft. Modern pumps are fitted with pre-packed ball bearings, which are sealed at each end to eliminate the need for lubrication.
Impeller type water pumps must turn rapidly to be efficient, and worn or loose drive belts can permit slippage which is not easily detected.