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How To Replace A GMC Water Pump

The water pump in your GMC is responsible for keeping the water circulating throughout the engine components in order to keep them cool while the engine is running. Here's how you diagnose and replace a failing water pump on your GMC.

1. Weep Hole Leak

The weep holes are two holes in the casting. The top hole is an air vent that keeps humidity from building up around the bearing. The bottom hole offers a place for fluids to collect and drain, which protects the bearings. If you have a horizontal centrifugal pump, there is very little space between the seal and the bearing, and that gives fluid a place to accumulate. Both weep holes ensure that the seals stay sealed by allowing in atmospheric pressure.

It's part of a seal's design to drip a little bit. It has capillary action that will draw the fluid from the face of the seal, and this drip keeps the seal clean by removing dirt and debris.Sometimes, these seals fail prematurely, and there are a few reasons:

Temperature: If your engine runs hot or overheats, the spring-loaded assemblies in the mechanical seal may disintegrate. If the system runs dry, the seal faces can warp. When a seal face is worn, warped or otherwise damaged, the fluids will leak out the weep hole.

Electrolysis: There may be filming or crystallization on the face of the seal that will allow fluid to run into the weep hole chamber. This is usually found in high mile vehicles due to a pH imbalance.

There are corrosive inhibitors on the plate metal surface, and these silicate levels can reduce with time. That makes the coolant more corrosive to the plate metal and creates electrolysis. The recommended flush and fill schedule is usually 24 months or 30,000 miles.

Additives: Some additives can cause a concentration of gels on the seals. These deposits can cause the seals to fail.

Abrasives: Any time you have any abrasives in the coolant system, you can cause a seal to become damaged.

2. Broken Housing and Shafts

Excessive vibration can cause the housing or the shafts to become broken. Some of the more common reasons there is excessive vibration include the following:

  • Fan is not mounted squarely
  • Fan is broken, cracked or bent
  • Pulleys are bent or cracked because they were improperly installed or handled
  • Belts have been over-tightened, and that caused an overload on the bearings and off-center rotation.

Water Pump Replacement

If you decide that you need to change the water pump on your GMC, follow these instructions.


  • Basin for old fluids
  • New antifreeze or coolant
  • Replacement water pump
  • Socket wrench
  • Shop towels
  1. Disconnect the negative battery cable to avoid sparks or shocks.
  2. Place a clean basin under the radiator and remove the drain plug on the bottom of the radiator in order to drain all the fluids. Keep the fluids clean, as you will be putting them back into your vehicle.
  3. Use an adjustable wrench and remove all the connections to the water pump from the belt, clutch, fan, hose and ducts.
  4. After you have removed all the attachments, loosen the bolts on the block that holds the water pump. Take off the gaskets that are between the water pump and block. Throw them away. You will be using new gaskets.
  5. Use a scouring pad to clean all the edges on the new pump in order to eliminate any metal splinters. Be sure to add your new gaskets.
  6. It is recommended that you add a high temperature sealant onto the block before you place the new gaskets and water pump on it.
  7. Once you have the water pump in the proper position, bolt it back onto the block. You can now reattach all the parts you disconnected. While you are replacing things, check your hoses and other parts to ensure that they are all in good shape.
  8. After you have everything reconnected, replace the drain plug in the bottom of the radiator, refill it and add new coolant.
  9. Reconnect the negative battery cable and start your engine.
  10. Make sure that your new water pump is operating properly, and check for any other leaks or parts that may have not been reconnected tightly.

If you run into any issues or this does not fix your problem, you may need to consult with your local dealership for more help. Always replace your water pump and related components with genuine GM parts to prevent premature wear or failure in the cooling system.