Here is the breakdown on Ethylene glycol antifreeze at sealevel.
Boiling Point B.P.
Freezing Point F.P.
Pure Water B.P. 100°C / 212°F F.P. 0°C / 32°F
Antifreeze/Water 50/50 mix B.P. 106°C / 223°F F.P. -37°C / -35° F
Antifreeze/Water 70/30 mix B.P. 113°C / 235°F F.P. -55°C / -67° F
Increasing altitude decreases the boiling point of water.