Last winter and this winter I've had a cooling problem. I don't have an aftermarket gauge. It seems to run warmer in the cooler weather. Recently it's been running about 3/4s up. Over the summer it ran in the middle. Even when I would really get on it, it would never read this hot. Once and a while, I noticed that when I stop, it will go down just below the halfway point. As soon as I hit the gas it shoots back up. Is it just a problem with the sender or gauge?