The freezing point of the coolant varies according to what proportions of antifreeze and water there are in the coolant mixture. Also, teh boiling point changes with the antifreeze concentration.
Most vehicles require a 50/50 mixture of antifreeze and water for normal operating conditions.
If you look on the side of any antifreeze jug, it will have a chart printed there that shows the actual boiling and freezing points for different concentrations of that particular brand of antifreeze.
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