I have a 2005 Honda Civic with 150000 miles. I was out of town and on my way home about 200 miles in 100 degree heat with my AC blasting. My temp gauge is always at the 1/4 mark. Well the last 20 miles of my trip the gage went to 3/4 so I shut off the AC and turned on the heater and the gage went to 1/2. But every time I stopped at a light it would shoot up almost to the red line. What could be wrong? Or just a fluke cause I was running it so hard?