Another thing that
antifreeze does is provide corrosion protection for iron, aluminum, and brass parts of your cooling system.
Just run your car for a week on straight water, then drain it into a pan. Not very pretty, is it? That's rust from the inside of your block and heads.
Run a 50/50 mix year around. Flush and change it every 3 years. Like Don & DV said, if it overheats, fix the problem.