I just got back from a 5 mile trip to the auto parts store. On the way back, my temp spiked from 180 to almost 250! I pulled over and shut it off. There was no steam or anything. There was coolant in the overflow still. Everything seemed normal. I started it up and drove home. On the way it spiked a couple of times then quickly went back to normal again. I was thinking there might be bubbles but I had flushed the system a while back and drove many miles since with no problems. I replaced the thermostat (180), hoses, and radiator a little over 6 months ago. I don't get it. Both my Scanmaster and my temp gauge read the same and I assume they aren't on the same sending unit. I don't know.