I've got a 02 1.8t GTI and I was driving on the highway the other day and noticed something. My temp gauge started climbing a little so I threw the heat on and it went down to 190 again. As I got closer to work I started to play with it to see if I could determine what caused the problem, I turned the A/C on and the temp gauge started to climb again so I threw the heat back on, nothing was leaking or anything either so could it be the thermostat? If not, what could it be because I need to get this fixed asap. Thanks guys..