So, I replaced my UIM with a Dorman, and replaced the LIM gaskets with the upgraded aluminum ones last weekend. I also flushed the cooling system out and replaced the thermostat, cleaned the throttle body and all the sensors out, re-sealed the injectors, and replaced the plugs and wires (Delco wires and TR55 plugs). It runs really great, starts quicker than before (and with more authority!) and idles perfectly (buttah smoov, yo) but it seems to be running hotter than before. The thermo I used was a 195. I didn't drill it, but I tried to bleed the air out as best as I could. I'm not seeing any signs of air pockets. My mix is about 60% GM approved coolant.

Before, it would always hover around 200 degrees on the dial, occasionally going up to about 220 and then dropping back. Now, it seems to be pegged at 220, occasionally going a few degrees over, and then dropping back down to 200, and then going up again to stay at 220 for a while. Seems to be zero danger of it overheating.

Not a real big difference, but it is basically running 20 degrees hotter all the time, and I can't figure out why. Is this normal? Did I maybe have a cooler thermostat before? Help, as always, is appreciated.

I suspect that you may still have to do some more bleeding/burping of your coolant system. Take a read of this procedure in TECHINFO:

Coolant Fill Procedure for the L36 3800 S2 Engine

I noticed today that my upper radiator hose was leaking. Fixed that up and made more attempts at bleeding the air out and things seem to be about right.

I did my UIM/LIM and had significant problems bleeding the coolant system. The engine ran WAAAY hot until I got it bled. I don't know why mine took so much to get the air out but it did. Once the air was gone, no problem. I also chose the 180F thermostat.

That 60% coolant may be a bit too rich also. And why are you running DEX after all the top end work? It'* half the problem. Get it out of there ASAP if it'* actually DEX.

Dex? What the hell is Dex? :p

Its green Prestone that meets the GM 1825M (or whatever it is) spec.

Considering you haven't put your year and trim level/model in your signature, we have no idea what you have. So the general warning about DEX is posted.

Can you please update your signature?

I think I can do that for you.

How'* that?

at hte top of the page, just right of center, clickon PROFILE.
Then scroll down a little to the Signature section and fill it in with your car info
Then scroll down to the bottom and click SUBMIT