Ok here goes, recently in houston it has been cold so I paid it no mind that the car would not warm completely up, but now temperatures are starting to go back to normal and now If I fully warm my car up the car temp gauge will rise to operating temp no problem and never pass the half point, now If I just warm it up lets say from cold to the bottom of the temp gauge and start driving, then the gauge just stays at the level that I warmed it up to and never gets to the halfway point on the gauge. It sounds like my thermostat is stuck open, but I just wanted to get some suggestions.

 

Sounds like it to me...easy to replace to.