Inability to operate the water pump leads to severe loss in the engine due to heat, and there are three ways to test the functioning of this pump while mounted on the engine; if it is discovered to be faulty, then, it has to be replaced with a new one or a rebuilt one. If the water pump is Okay the pressure, to the upper hose, should rise when the engine reaches normal operating temperature and the hose is squeezed. Water pumps have weep or vent holes which, if the seal of the pump fails, coolant leaks from these holes and to identify the leak on the underside of the water pump, requires a flashlight and mirror. Moreover, the failure of the water pump shaft bearings may cause a howling noise from the drivebelt zone when the engine is running, and even shaft wear can be sensed if one rocks the water pump pulley up and down; although error may be made with drivebelt slippage which whistles Slide .