because when cooling water is freezing it increases its volume and causes cracks in the engine block
and #coolant pipes .When a substance is dissolved in water, the freezing point of the solution is less than that of pure water, and the boiling point increases. This change relates to the concentration of the dissolved material. This phenomenon is exploited by spraying salt on snow or snow-covered roads cause melting of ice.
Glycerol is used as an antifreeze agent and is used in 60-70% of the solution. The freezing temperature is reduced to -37.8 ° C
The antifreeze has another benefit of reducing corrosion and rust in the cooling system