Every time I drove the car, the fans would run after I parked. General consensus seemed to be that the thermostat was bad. Replaced it, and obviously did something wrong. Driving through the city, temp stayed at its normal 45%. As soon as I got onto the highway, it started climbing. Immediately cranked the heat, and it hovered around 60%, fluctuating rapidly based on speed and grade of the road. Can anyone help me fogure out what I screwed up? Thanks for the help everyone!

 

It would help a lot to know what year/model the car is. Chances are, you either got the wrong thermostat, or you didn't bleed the air out of the system.