I'm new to this site, didn't know what else to do since I couldn't figure out how or what needs to be fixed. So Friday I was driving to work and noticed the service engine soon light on as well as check gage light. I looked at my gages and saw nothing weird at first, then noticed that the engine coolant temp one was acting weird. It will start at 100 when I start it. Drive for a few minutes it will be at the middle line between 100 and 210. I went around a corner on Saturday and it went back to 100 then to the in between line again. It does get up to about 210 where it normally is after a while but it will still go back and forth with the in between spot. Even when slowing down for a stop. Last night when I coasted somewhere it seemed to move all around too. Sunday on my way home from work I noticed even when I was hitting my gas it would go down sometimes close to 100. What is causing this? Coolant level in its tank is at the line. Any thoughts would be great! My friend deleted the check engine light code and didn't tell me so I don't know what it was.

 

Has anyone had this happen to them? My check engine light has come back on now. But the gauge would go from 210ish to 100 when I turn a corner.

 

I had many problems when I had a Trailblazer. On mine and a friends the thermostat stuck in the open position and the engine never came to operating temp with the check engine light.. It was too much trouble to change the thermostat so I left it alone. It ran fine. You have to remove too much to get to the thermostat. Another problem I had and it sounds like you are also having it. The stepper motors for all of the gauges go bad and need to be replaced. $600 if the dealer does it. There are places that will do it for you if you send them your gauge cluster. You can do it yourself if you can solder. Not very difficult.