Since the cold weather has set in, my car has been having trouble reaching operating temp. I have a 180* t-stat installed, but it will only go about as high as 170*, if I'm lucky. Is there a possibilty the t-stat is stuck open? I would think that the engine would reach at least 180*, then the t-stat would open/close when necessary to maintain temp. What exactly controls the t-stat's opening and closing?