I have a '90 XR7 and it is heating up way too hot and then all of the sudden the temp drops and the heat starts to blow. It did this about five times. So i figured it was the thermostat. I replaced it with a 180. same thing. I start it up all the coolant goes into the puke tank and it acts likes the thermostat isn't opening. I was told by a couple of people that the water pump took a crap but I don't see how. has anyone ever heard about a water pump where the impeller comes loose from the shaft? What else should I check?? MAybe I'm not filling the radiator right, but I really don't think so. It could be an air bubble, right? I hope it's not *ulp* head gaskets. I just bought the car last week. If any one has had this problem please reply and let me know what to check.