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Q: How do you know if your water pump is bad on a gm3400 v-6? It is not leaking, but continues to run hot with a new radiator/stat.

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I have replaced the thermostat and radiator in the car, but it continues to run hot even after I have bled the air out of the system. Thinking maybe the water pump is bad, however it is not leaking.

My car has 230000 miles.
My car has an automatic transmission.

The cooling system on these cars are notoriously difficult to deal with. I have extensive experience with this model of vehicle, and I can say with confidence that getting the cooling system bled can be quite hard to do at times. A lot of times, getting the air out of the system requires the use of a vacuum fill setup. The kind of setup that you start with an empty system, vacuum all of the air out of the system, and then the tool fills the vacuum directly with coolant. The cooling system on these cars are literally the hardest to bleed that I have come across in my 30 years of experience. With that being said, if you are sure you have all of the air out of the system, you can pull the radiator cap, on a cool engine, and you should see the water pump cycling the coolant through the system. You can also pull the belt and check the water pump pulley. Check that it doesn’t have any wobble in the shaft, from a failed bearing, or a broken shaft. One other thing to mention, the cooling fan on these vehicles are also notorious for failing. Be sure to check that the fans come on at the correct temperatures. If you have any doubts about how to do anything I’ve listed, or the results that you’ve come up with, be sure to consult a certified mechanic, like those available at YourMechanic.com.

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