The whole winter here in Utah the temp gauge in my 200 '65 mustang would warm up to just below midway between hot and cold. Then just recently the temp jumped up and was near the hot mark on the gauge. It never over heated. Then yesterday I started my car and it idled between 1 to 2 minutes and the gauge was dead center between cold and hot. Which is really fast time to warmup, to me, especially at an idle the whole time. I don't know if I can trust the temp gauge or not. My question is, how can I check the temp on my car? I am planning on replacing the thermostat just in case.