My 98 Stratus for the past week has been heating up very quickly, just today after about 15 minutes at 40-50 mph I had to pull over because the thermostat gauge had reached the top. I'm not sure why it's overheating. I just topped off the reservoir two weeks ago and it doesn't seem to be leaking coolant. I used the right kind and it was pre-diluted. I don't know if this has anything to do with it but around the same time the heat stopped working in the car. Feel free to ask any questions I just want to get to the bottom of this.