Water, with the proper anticorrosion additives, would make an
adequate cooling medium for automotive engines. But it freezes, and boils over. Ethylene glycol, an alcohol, is added to extend the boiling and freezing points of the coolant. Why not run
pure glycol, and get better freezing/boil-over protection? As you can see from the chart, pure ethylene glycol will freeze at essentially the same temperature as water. At concentrations
higher then 70 percent or so, freeze protection is not very good. Also, ethylene glycol doesn't carry as much heat from the engine to the radiator as an equivalent amount of water,
which can result in overheating. Stick with concentrations of 50 percent to 60 percent water/antifreeze or go to a non-aqueous coolant.