Hey Dave...Remember that thermostat you sent me a long while back? Yea... I got around to using it and guess what!? It's good! It rises to 200*F and lands back to 193*F and holds steady. More testing to follow!

Was a cummins t stat? I got to see an old style cummins t stat monday. That 2000 wreck I bought had one and it is a different looking piece.

Pretty sure its a NAPA.

If my memeory seves me correctly, I googled the part number and it came back as a tstat for an 03. Not sure where I bought it, but the only Cummins stat I bought was a 180* and I still have that one. My problem must lay elsewhere. Glad it worked for you. If I ever get my problem solved i want have to buy another tstat for a long time. I have a nice collection of tstats and a couple spare ECT sensors to boot.

Ummm... Owner error...:lmao2:Seriously I've only been out once with the truck and the initial opening of the thermostat was right at 200*F and then it feel rapidily to about 186*F closed again then came up to 193*F and stayed. This was only a 10 mile round trip to the dumpster. So more testing to come. Oh yeah you right really don't loose much coolant pulling the thermostat cover off. I figure there would be more loss and mess.

My brother owned a Buick Someset many years ago and the tstat was under the radiator cap on a long handle. Just pull the cap, pull the handle and reinsert same and you were done. The wifey's Dakota is on the underside of the engine. It has a reverse flow cooling system. its really messy.:cry:As far as that tstat you have, I just went in the parts house and asked for one for an 02 and thats what they gave me. It looked right so I put it in. Worked as crappy as the rest. But since it worked in yours, the problem must be somewher else. I have got to change my heater core so I will be draining everything pretty soon.