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How to Test a Water Pump

Nathaniel Miller

Water pumps are what keep gasoline combustion engines from overheating as you drive your car or truck down the highway. The water pump circulates water through the engine to keep the internal components from overheating and seizing. Because of the water pump's often hard-to-reach location on the engine, it may seem difficult to determine whether the water pump is bad or not. However, it is actually relatively easy to test a water pump for failure and even the most inexperienced mechanic can perform this troubleshooting test.

The water pump impeller is what keeps the water flowing through your system.
  1. Open the car hood and locate the thermostat on the top of the radiator lid. Pull the thermostat and start the car. Watch the temperature gauge carefully. If the water pump is working properly, the engine should take a long time to warm up (if it ever does). With the thermostat removed, the coolant should circulate continuously, making it harder for the engine to warm up. If you cannot tell if the car is heating up slow or not, move to Step 2.

  2. Turn the car off and locate the water pump and the water pump drive belt in the engine compartment. Use the wrench set to loosen the belt retaining bolt and pull the belt off of the pump. Spin the belt drive with your hands to see if it rolls smoothly and to determine if there is any movement or "play" in the driveshaft. If the pump seems in good working order, replace the belt, tighten the retaining screw back up, and move on to Step 3.

  3. Locate the coolant drain plug on the bottom of the radiator and use the wrench set to remove it. Allow all of the coolant to drain out into a container and dispose of it. Replace the drain plug in the bottom of the radiator and then pour coolant into the radiator. Start the car up and watch the level of coolant carefully. If the water pump is working properly, the coolant level should drop quickly as the pump circulates coolant to other areas of the engine. Fill the radiator back up with coolant and watch it to drop again. If the coolant drops then your water pump is fine, however if the coolant drops very slowly or not at all it may be time for a new pump.

  4. Tip

    When in doubt, it is best to replace the water pump as a failed water pump can easily destroy an engine.


    Dispose of the coolant in a sealed, municipality approved container as the contents are harmful to humans and animals alike.