[Evans, Marv]

I've always understood part of the importance of using a coolant mixture was for its lubricating properties (water pump for one thing) and the fact it can hold more heat in terms of calories than water by itself (don't know the validity of that though). I can't actually understand why you would be using water only. An off the wall thing that sort of matches the symptom your car had was something a friend of mine had. The car would apparently over heat occasionally. If she stopped and shut it off for awhile, it would be OK. Turns out she had the coolant changed and the change left an air bubble in the area of the heat sensor that would seem to be circulated around and occasionally settle on the sensor and register an overheating situation. She had the coolant changed again & the problem went away. I had a hard time believing it, but couldn't deny the problem disappeared after the coolant change.