Signs of impending failure: Seal failure can usually be foreshadowed by bearing failure, but not always. A sure sign of bearing failure is a noise coming from the water pump. It can be anything from a deep growl to a high-pitched squeal. As the bearing wear gets worse, it will eventually allow enough shaft movement to take out the seal. On the bottom side of the shaft housing is a small vertical hole. When the seal leaks, coolant will exit this hole. Generally, at first all you may notice are a few drops of coolant under the vehicle. This can, in a matter of minutes to weeks, develop into a strong stream.
Something else to keep in mind and not confuse with a bad water pump is a leaking radiator hose where it mounts to the water pump. Sometimes without some serious detective work, it's hard to tell the difference. Don't confuse a bad bearing squeal with noise coming from another one of the accessories, the belt-tensioner bearing, or just plain belt squeal. A belt that is too loose will squeal at engine start-up or when a load is placed on it, such as the A/C pump locking on or when turning and the power steering pump is activated.
Misaligned pulleys will cause the belt to squeak, usually at a rhythmic rate. Oh, and that "belt dressing" they sell in auto parts stores? Don't bother-it's just a temporary cure. As it wears off, the belt noise will come back. Fix the problem. Sometimes, if the belt has been slipping for any length of time, it will become glazed. Once this happens, the only cure is to replace it.
Another sign of water pump failure can be with the vehicle overheating. If the radiator is known to be in good condition, the fan and shroud are matched and properly positioned, and nothing is blocking airflow through the radiator, do consider the water pump. Impellers, depending on the type, can be damaged by corrosion or the ports partially blocked by corrosion. Generally speaking, if you need to replace the radiator, it's also time to replace the water pump.
Regular coolant changes to keep the radiator clean, providing the proper additives for lubricating the water pump's seal, and making sure the pulleys are in alignment and belt tension is correct-all will help to ensure a long life for the water pump.