New CTS & Thermostat replaced RPM goes up and down still

Your coolant level should go up as the engine temp goes up and draws back down when it cools. I would first suggest you check the fluid level at the reservoir and fill if needed. Once that is established, then you might want to try bleeding any air captured in the system when you changed the Tstat. Do that by running the car a few minutes with the radiator cap off. If the fluid level in the radiator drops, add more and recheck the level in the reservoir after replacing the cap.

I was able 2 refill Reservoir 3 times but now car won't start in I put a new thermostat any new coolant temperature sensor in finally when the coolant started to go down car sounded good I turned it off to let it sit so the coin would go down again the 3rd time now the car won't start I put a new massive air flow sensor in it 2 months ago also new fuel pump and Throttle position sensor you name it it's new in the car why isn't this card wanting to start I have a code but it's just reading thermostat or then it will read only call in temperature sensor circuit high

Sorry I used voice to message because there was alot to say and I just re read it and It made a few errors. I have no idea why my car is reading coolant temperature sencer Circuit high, but then the next day it only reads something about the thermostat. But now that there more coolant in the system I'm gonna let car sit for tonite. With it not wanting to start its flooded itself out. I'll try again tomorrow and read what its saying and I'll get back.