Yes, but the heat transfer effectiveness diminishes. This is of no consequence for a properly functioning cooling system. Pure water would have the "ultimate" heat transfer effectiveness. Of course, pure water would be unacceptable, so cooling systems are designed for the reduced effectiveness of the water/glycol mixture. For an overheating cooling system though, you can't sacrifice heat transfer. In fact, the rust mad in the coolant has about the same effect as antifreeze in increasing the boiling point. The 16 psi cap also retards boiling to a temperature that will hopefully never be reached, even with overheating. D^2 At 01:07 PM 4/20/2002 -0700, you wrote: >actually, adding more antifreeze will raise the boiling point of the >coolent & it >won't boil over so easily. The ideal ratio is about 50/50. >John