- An auto's water pump failure is usually caused by a bearing failure on the pump shaft accompanied by a water leak. The water leak is generally witnessed coming out of the weep hole at the bottom of the pump. There can also be a leak around the gasket located behind the pump. At times, water pumps have be seen to leak at a certain spot on the bearing surface. A water pump definitely does not leak when the engine is shut off, so it must be pressure tested when the engine is running.
- In almost all cases, a bearing failure will cause the pump shaft to be loose and can be tested by grabbing the fan and wobbling it. If the pump shaft moves when wobbled, it is obvious the shaft is worn out. The water pump will also give an audible signal that is easy to detect. Care should be taken to replace the water pump as soon as possible since it can lock up, causing the accessory belt to come off. If the belt comes off, in many cases, you will also lose power steering. On occasion the pump will break and possibly go through the radiator and ruin the radiator as well.
Use a radiator pressure tester for this test. Remove the radiator cap when the engine is cold. Fill the radiator as necessary to bring it to the normal level. Pump the pressure tester up to 15 pounds and look closely to the water pump for leaks. If any leaks are present, the pump needs to be replaced. While the pressure tester is pumped up, check for leaks in the radiator, hoses, the top of the engine for intake manifold leaks, the side of the engine for freeze plug leaks and at the heater core. - One more area that should be tested and considered is the pulley on the water pump. While this may or may not cause a leak, it can cause the water pump to stop working. Check the pulley for out of round or warpage. This could cause an out of balance condition that rapidly wears out the bearing in the water pump. Start the vehicle once the pump is replaced and watch the water pump pulley to see if it bounces. Replace the pulley if it shows out of round. Also check the fan for form and function and replace as necessary.
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