A coolant pump is a type of pump used to recirculate a coolant, generally a liquid, that is used to transfer heat away from an engine or other device that generates heat as a byproduct of producing energy. It's basically a very simple centrifugal pump containing an impeller within a metal housing ƒ?? the pump is driven by a belt from the crank and the pump's impeller forces the liquid out of the pump. The action of it forcing the water out, draws more water in.A mechanical pump as fitted to most engines runs continually, or at least all the time the engine is running. Symptoms of a bad coolant pump includes engine overheating, coolant leakage, coolant pump pulley making whining sounds etc