snsrushing

I drive it on the weekends and when no snow is on the ground, recently I noticed that I would drive it from home to work which is about a 15-20 minute drive. The temp. gauge never gets over maybe a quarter. Back in the summer it would eventually get to a the half way point but that was after driving for 30 min. or more.
I dont know where to start, I havent had any problems and it starts up and will run good. I just dont know what to make about the gauge.

I do have the AMF unplugged but its been unplugged for about 8 months and I never really noticed it until recently. When I had some work done to it I noticed my mechanic put the green anti freeze in it. I though it had the red stuff originally. Could this be causing the gauge to not work?