I have a 1977 Mustang II and it's been overheating a lot the past week or so. I'll get into it to drive to school in the morning and on the way the temperature gauge will go from cool to hot, then back to cool, then back to hot, then it'll idle in the middle for a little then go back up to overheating. It's really random. Sometimes it overheats when I'm at a stop light and sometimes it'll overheat when I'm driving 50 mph down the road. There's not really a pattern or anything to it. The fan is blowing fine (or at least it is when I'm look at it) and I just put more coolant in. So, I don't know what the deal is. What are some possible reasons that it could be doing this. Thanks a lot!