OK. Based on that, sounds like a T-stat hanging open or air in the system (but air pockets tend to cause the temp sensor to read high).

I would definitely change the T-stat. If you can do it, a coolant flush before hand and JC mentioned the coolant elbows, if they have not been changed, do those since you have to re-fill the system anyways.

 

Just popped CEL, not very warm today so im going the change the tstat out with as little coolant loss as possible and not flush the system.

 

Just had basically the same issue with mine about 2 weeks ago and after swapping the tstat its been running fine again.

 

Even with it being 10 degrees here my gauge still gets to the line above a quarter, thermostat opens a few lines before half. I'm sure you have it figured out just wanted to comment anyway.

 

Yeah replacing the thermostat did the trick.