Hi. I just took my car to the radiator man, and he told me my problem of the car running up to hot likely was from foam that builds up from antifreeze. Over the past few months, the gauge would go up and down, and I could tap it down, but this time I could not, and the gauge went all the way to orange. I had the thermostat replaced, which didn't make a difference. Also, at beginning of winter, my heat wouldn't get real hot, so I had the heater core replaced, and that didn't make much difference. I still didn't get hot heat. The foam was the most likely culprit, so first he checked with some gauge and saw that I had 100% antifreeze in the car, and actually my system calls for 50/50, which was the first mistake I made. He didn't flush the radiator. He drained out about half or more of the current radiator fluid, then added a remix with water. He added a bottle and a half of antifoam. When I drove there, same problem occurred--it was up to the orange in no time. When I left, the temperature ran below normal, and after driving a while it was right at the halfway mark. My regular mechanic was going to charge me $80 to flush out the radiator, and another shop was going to charge $125. So glad I called the original man back. My bill was $31.80, and that included $12 for the 1-1/2 bottles of the antifoam. YIPPEE!!!! Just thought I'd give you all an update. Thanks so much for all your responses! Susan