Correct me if Im wrong, but isn't the thermostat supposed to control the temperature of the car? If the temperature reaches the set level, the thermostat opens and allows coolant to circulate, cooling the engine. So if this is the case, how would water wetter make the engine run cooler, if the cooling system was already functioning properly? I have a very clean cooling system, a new water pump, and a 50/50 mix of water/coolant. In S. Florida on a 90 degree day with the AC on, it hits 85 degrees celcius on the temp guage... The same that you said for your car on a 75 degree day without A/C and being on the highway. So really, what difference does the stuff make if your cooling system functions properly.