Your car's water pump is as vital to the engine as your heart is to your body, and its function is similar.

The fluid the water pump circulates through the engine and radiator is coolant, a mixture of anti-freeze and water, that keeps the engine from overheating.

Sometimes a water-pump bearing will go bad; when this happens, the pump will eventually self-destruct. In some cases, the fan will chew into the radiator, damaging the radiator core.

If you hear a noise that you fear may be a bad water-pump bearing, or if somebody tells you the water-pump bearing is bad, how do you check it?

If your car has a conventional nontransverse engine, with the engine shut off and the ignition keys in your pocket (transmission in park, parking brake on), raise the hood and locate the fan.

The fan is fastened to the water-pump pulley. Grasp the fan blades and try to rock the pulley back and forth. If there is any movement in the pulley, the water-pump bearing is bad and the pump should be replaced.

Sometimes there may be a little play in the pulley, and the water pump may still last many miles before it finally gives way. But you're taking a big chance by not replacing the water pump. When it does self-destruct, which it eventually will if there's back-and-forth play in the bearing, you can end up buying not only a new water pump, but perhaps a new radiator and possibly other items.

Now if your conventional engine has a clutch fan -- with this kind of fan, the fan may not run all the time as it does in the case of a non-clutch fan -- you check the water pump in about the same way.

The big difference is that you may detect a little back-and-forth movement when you grasp the fan blades of a clutch fan and try to move them back and forth. This movement is in the clutch and is normal. Don't misinterpret this as movement of the water-pump pulley.

To make an accurate diagnosis here, look at the water-pump pulley itself as you wiggle the fan blades back and forth. If there is back-and-forth movement in the pulley, the water-pump bearing is bad. If there's no back-and-forth movement, it's okay.

On some newer cars the engine is mounted transversely -- crossways. In this type of car the fan is not attached to the water-pump pulley. So you must locate the water-pump pulley. Grasp the pulley itself, and try to wiggle it back and forth. The same deal goes. If there's back-and-forth movement, the bearing is bad. No movement -- everything's okay.

One last thing -- when I say try to move the water pump pulley back and forth, I don't mean try to rotate the pulley. You very well may be able to get a little rotational movement. Obviously when the engine is running the pulley will rotate, because the belt is making it do so.

By back-and-forth movement, I mean movement back and forth in line with the engine.

Again, be sure the engine is off, and the ignition keys are in your pocket (you don't want to lose any fingers). Have no rings or jewelry on your hands or arms (they might snag on something). And be sure the engine is cold. You don't want to burn your hands.