sounds right if you dont have anything like torque app or whatever to see what the pcm is reading.

Your right, won't go to limp mode unless the temperature is actually too warm (majority of the time anyways). The Northstars will generally read right at 200 on the gauge cluster, so your within reach at the temperature you posted. More than likely not the sending unit since it was working corectly before the new thermostat.

Checked the new thermostat and it opened at 180. installed a new sending unit...no change, next is air in the system. what is a good evac tool? I have found the "mightyvac". does anyone use this or something different?

Hmmm, I don't think I've ever seen such stubborness after changing a thermostat lol. Just a suggestion before you get an evac tool. Check to see if there is coolant in the hoses after the water pump. If there is nothing, it could be water pump that is your problem, but also could be air in the system. To see if it is air in the system, start the engine cold with a hose loose after the water pump and when you reach operating temp your coolant should push the air out of the line. When coolant starts coming out of the hose, re-attach it and see if you maintain operating temp. This can get messy so use preventative measures, but its free! Also make sure the heat on the climate control is blowing hot air. If no coolant comes, bad water pump. You could have a mechanic with the evac tool bleed your system to for alot cheaper than buying the tool also! Then of course, you have to get it to a mechanic...

Don't be insulted by my asking, but is there a bleeder screw on top of the thermostat housing?

turns out, it was the radiator cap. The shop did a pressure test and the cooling system was fine so he figured it was the water pump, so he took it out to replace it and it looked fine, so he put it all back together and vacuum filled the system, then tested the cap. Cap wouldn't hold pressure. So now its all running real good. Thanks to all who chimed in. And 2kg4u...nope no bleeder valve on housing.

I have an xlr-v with the actual running temp fine but the gauge is intermitent, it always sweep tests on startup but sometimes does not respond as the car warms up. Where did you find the temperature sending unit on your northstar.

Its on the drivers side, firewall facing head sorta under the throttle body. A real PITA to get to.