Water Pump Size (?) on 6.0L -

[Ol'Jim]

Getting ready to replace the water pump on my 02 HD2500 4x4 Crew 6.0L.
It is seeping, and with 245,000 miles on it, I got my $$ worth out of the original one.

My question is regarding the replacement pump. Most every parts store & website I have checked, shows 2 different outlet diameters: 1.88" or 2.05".
Is this gonna be one of those "Wait til you get the old one pulled off, bring it in and we will match one up for ya" type of deals?
Or is there any way of knowing which size I need, by using visual identification, or the VIN, or any other means?

Thanks in advance for any advice y'all can provide, I would like to have the new replacement pump in-hand when I begin the job on Saturday morning.

[j cAT]

the big hole is in your truck I am pretty sure. in around 2004 GM changed to the smaller . the T stats are the issue since you would have to use the one for the smaller bored new pump . my guess is the old style T stat is more expensive so GM changed the design. since you have had this so long check what T stat you purchased in the past then you will know for sure. also look up the pump using the model year pull the pump part numbers then compare with the 2004 plus pump #. it should show the bore diameter also.

[Ol'Jim]

This replacement went smoothly, my first W.P. job on an LS style engine. Fairly straightforward, other than the unusual screw-on fan blade/clutch assy. (I have seen many trucks with electric fans, so they would not have this step in the procedure). I did not have the pulley holding tool, so I hit the threaded coupling with some P.B. Blaster, tapped on it, sprayed again, let it sit for a few, then used a pipe wrench on the large hex, and did sort-of an "impact" technique, tapping the wrench with a hammer, while pressing down on the serpentine belt to tighten it up and prevent the fan pulley from slipping. Came loose fairly easily using this method. I reinstalled the fan/clutch assembly the same way.
I bought a New replacement pump, these days it is worth the extra cost, as I have seen so many poor-quality remanufactured assemblies, (water pumps, starters, alternators, etc). The one I purchased was a Murray P/N CP5104. Lifetime warranty, from O'Reilly. It is Chinese, (as is almost everything anymore). It did have the larger bore, so I reused my thermostat, since it was still working fine and a large percentage of replacement thermostats are defective. I compared the castings of the GM and Murray pumps, and it appears to be of rather decent quality, I noticed some enhancements vs the original.
Only thing I was a bit disappointed in, is that it came with paper gaskets, where the OEM pump had gasket "plates", (thin steel shims, with rubber O-Rings built-in around the water passages, so no sealant was required with those). I carefully cleaned the block surfaces, and used a thin, even smear of good quality Permatex RTV on both sides of the gaskets. Used an Inch/LB torque wrench, since the bolts are so small, and the torque values so low. Re-torqued them again after about an hour, (they did move some more after sitting). Filled it with 50/50 Dexcool & distilled water. 2-1/2 weeks later, have driven it just over 900 miles, (including a fair amount of highway, and stop/go heavy traffic in 90* weather), no leaks, no problems.