Took a long trip the other day and didn't notice anything but on the way home almost home i noticed the temp at about 250 not maxed out. I popped the hood after i killed the engine and didn't hear anything nor did the engine feel hot, the fans were running. I waited until the next morning to look again and noticed that the reservoir was almost empty and the return/overflow line had come off, i put it back on and filled it up with Dex Cool. ran it for awhile ran on 210. My wife went on a 20 mile trip and on the way home it went up again.
I am at a loss to figure out what is happening.

 

Did the return/overflow line come off again? Is the coolant level low again? Look for small leaks in radiator or any of the hoses.

 

I will look today, could the system have an air bubble?

 

Air bubbles don't stay forever in a good system. After adding coolant once or twice after driving it, the air bubbles should be gone.

 

I got letter from Chevy the other day saying to watch reservoir level as the water pumps have been weeping through shaft. They state that they will replace the pump if it gets to bad. My 09 does need refilling every 700 miles.