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Water pump bearings banging?

2000 GMC Sierra 2500 6.0L gas engine 150K miles. After returning home from a 150 mile drive, I notice a very heavy sound of marbles banging around near the front of the engine at idle. The noise is a much like heavy detonation where timing is badly off kilter. Used my stethoscope to determine this is loudest at the water pump housing. The belt runs smoothly with no sign of unusual resistance. The engine does not overheat, and there is no sign of a coolant leak.
Can a bad water pump shaft bearing make such a tremendous “cackling” noise?
What else could it be?
Thanks for any ideas.

Yes, it can

The good news . . . this water pump is quite easy to replace

You’ll just need a special tool to hold the pulley, while you use your 36mm open end wrench to loosen the fan clutch

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Is there a timing chain behind there that could be coming loose and banging against the cover?

Thanks for confirming.
It seems odd that a ball bearing could get that loose and not just seize up entirely.
Access does look pretty easy.
36mm wrench is a few sizes bigger than I’ve got, but maybe my 1 1/2 will work.
Looks like I’ll be driving the Ranger for a while.

A 1 7/17 will work a lot better.

Pull the belts loose and spin the idler pulley(s) by hand. They can make a lot of racket - much like what you are hearing - when they are dying. Not sure about your 6.0 but my 5.3 has 2 idlers, one on the main belt and a second on the AC drive belt. Check those first.


I had a similar problem on my truck, and thought it was the water pump. It turned out to be the timing was a tad askew due to a vacuum advance problem on the distributor, and the noise was the engine pinging. Had nothing to do w/the water pump. Even though it sounded (with a stethoscope) like that’s where it was coming from. So don’t discount the pinging possibility entirely, as pinging can do some serious damage to the engine if left to its own devices for a long enough time.

I agree with @Mustangman - remove the belt and spin everything by hand, bet you’ll find the source.


Thanks for the suggestion. I will pull off the belt, check pulleys, and run the engine briefly to see if the noise persists. That should confirm or rule out detonation.