A 50/50 antifreeze/water mix protects to -37 degrees F. A 70/30 antifreeze/water mix goes to -69 degrees. Straight ethylene glycol without water in it freezes at +9 degrees, so a 70/30 mix is the strongest solution that's reccomended.
Good point Jerry. I've seen several instances where people assumed more is better and found out the hard way that the coolant turns to a gel above 70% and quickly destroys engines when it won't flow even on the coldest of days.
