So before i bought this car my sister was using it and the water pump took its life, Have no clue if the car overheated or if it went close to home (typical oh no daddy it was fine i checked all the gauges)

My dad replaced the water pump with a napa pump, after that the temp gauge once the engines warmed up will rise rapidly to just below red upon deceleration. Once you accelerate the gauge comes down. WE HAVE HAD A GOOD LIVE DATA SCANNER ON IT. While the gauge is hanging way up there the ecm is reading normal, right around 200* and solid. No coolant boiling, no steam, no oil in coolant and no coolant in the oil.

Have lurked around here for a bit and heard the stamped steel fins on the aftermarket pumps cant produce the flow of the original GM cast fin pumps in the DOHC engines. I bought it cheap figuring it was gonna need head gaskets but once i started messing with it all signs point to no. For the money to tear down and have the heads gone through(needs valve seals anyway, my thinking is i'd rather just swap a 3800 and not waste the time and money with this one. Now my thinking is as you raise rpm the pump moves more coolant (hence why the needle comes down) but as the rpm drops it doesnt flow as much and the needle raises. He even said the pump he took out had cast fins and the one he put in had pretty cheap feeling steel fins.
I have spent months bleeding the system, even draining completely, opening all bleeders and refilling. Coolant mixture is good, cap, superstat and the sending unit for the gauge were all replaced before i got it.

Is my hunch that it needs a OE GM pump a strong enough one to fork out the 170 bucks for a new pump? I have thought to put a regular independent gauge in it, but to me that seems like the half arsed way of doing things. Any ideas?

 

And while we're here, is this orange pigtail supposed to be plugged into anything? really really hoping that will solve my problem but i cannot find anywhere it would go

 

Drove it to work this morning, temp gauge reading towards the top of "safe" range, coolant temp via ecm at 210* Upper hose had coolant surging. Still seems like air trying to work out?

 

If the gauge goes down while accelerating, I would say there is air trapped in the system.

 

It does sound like air in the system, or a restriction. Has the radiator ever been replaced?

 

Well guys decided to go with my gut on this one(hasnt led me wrong so far yet) Picked up the water pump from the local gm dealer, got it swapped out and low and behold no problems now. Drove it around for quite a few hours and never got above 1/4 way up the gauge while driving and not even to halfway up in stop and go. Problem solved and i am now happy

 

Congrats man.
I got late to the party, I was going to suggest to bleed the coolant and replace the T-Stat, but glad you won't be needing to.

 

Yea i had bled it to the point i was 100% sure there wasnt any air in the system, and the lower intakes had been previously replaced but wasnt showing any kind of mis fires or anything.
Heres the aftermarket napa pump on the right next to the GM pump i picked up today


Had heard about the pumps somewhere not sure if it was here or somewhere else, not my first rodeo in the auto world by anymeans, actually suprised my dad didnt question the difference when he replaced it originally, he is super **** when it comes to this stuff, but he was in a bad place with some family drama and other stuff so may have just said oh well.

 

I looked up the water pumps on Rock Auto for my 02 Monte LS. And the $90 AC Delco pump looks like the one on the right in your pic. The $20 AC Delco pump looks like the one on the left in your pic.

 

They told me there was the oe replacement(left) that was 170, then a "aftermarket that was covered under the gm warranty" for $53. That was through the dealer i didnt shop around due to needing to get it on the road quick.

Just to update been driving it around since without any issue!!