Most water pumps are replaced because of noisy bearings or coolant leaks from the   water pump vent hole. On rare occasion, impellers may corrode or detach from the pump shaft.

Whenever a timing belt is replaced on an overhead cam engine, a new water pump should be considered. A potential water pump bearing failure could result in the teeth being stripped from the new timing belt—with disastrous effects!

It is good advice whenever changing a water pump to inspect all tensioner pulleys, air conditioning compressors, fan clutches, alternators, power steering pumps and air injection pumps for bearing and pulley wear. Mis-aligned pulleys can cause excessive belt wear and weak or worn bearings can result in serious system damage.

Whenever water pumps are replaced, the system should be thoroughly flushed and refilled with a 50/50 mix of anti-freeze and distilled water. Never reuse old coolant.