Anyone know of the best water pump to use?
I've replaced it 2x's in the last 6 months(ac delco)

 

How many mile's were on the original , then your source of parts is suspect , ac delco used to be good , but as time has past so has there sourcing [ lowest bid ] .
I would also worry about whats making them go bad that soon , even with moderate quality parts , bad water , coolant ???
With out more info , miles ect. its hard to figure .
As for quality , Find your local Cummins dealer , but better pricing at a equipment / farm tractor supply , same good parts at both .

 

as for miles the last one went 30,000 miles and I use z-05 coolant.

 

Again with out more info , I can not say , except that is too short a life , as for coolant , use just a regular name brand , non of the ultra millage / life time ect. , and not a premix , all of those have too high a cost and no real improvement , in fact what GM put in for yrs. [ red Dex ] was causing many issues .
Then only use distilled water & 50/50 mix .
Just a thought , there may be a very small combustion leak , causing issues with the coolant / causing early failure .

 

I don't think the shop used distilled water.

 

Distilled water is not going to a lot of difference , I just mentioned as a good think to do , when replacing coolant .
Also in a shop , its hard to have that much distilled water on hand , so it would be normal to use tap .

 

From what the shop and what I have been able to find out, the G-05 is the recommended coolant (aside from the dealer). I had 95k on the orig wp before it went bad. I replaced it with the one from Napa Auto Parts, which they said for the new part (vs. rebuilt) that there was a lifetime replacement warranty as long as I had my receipt. About 4k mi later, so far so good.

The service interval for changing (for my '04) the coolant is every 60 months (or 100k miles). I'll probably do a shorter internal that this, but that's me. Also, when I changed out my wp, I had the entire system flushed out. You never know, if some debri got into the system, that could contribute to the wp early failure. Also, I changed out the thermostat.

 

Serviced manual calls for distilled water. Where I live I sure as heck wouldn't want tap water in the cooling system.

 

Water and coolant is not the issue.Either just bad pumps as they are pretty darn simple and are not known to be a issue on these motors or belt tension er is causing a problem and lots of belt pressure on the pump.I worked YEARS(70s) back in a GM store that unless housing scored the MECHANICS(called them that back then) pulled leaky pumps,used a press and replaced the seal/bearing and spray painted them and put them back on.We did hundreds and hundreds of them over the years.Pretty simple thing water pumps for the most part.