Water is a far beter heat transfer agent that
antifreeze.
Antifreeze does lower the freezing temp and raise the boiling point. Ideally we could use just water with a corrosion preventing additive, but some of you live where it gets cold. Water wetter does help prevent localized steam pockets around the combustion chambers in the water jackets, it also prevents some corrosion. Adding it to a 50-50 mix will do almost nothing to lower temps however. It just allows you to run less
antifreeze (or none) so your coolant will have a specific heat closer to water instead of the lower specific heat of say ethylene glycol. Most organics (ethylene glycol, propylene glycol, and more) have a specific heat less than 1.