Why do you need antifreeze in your car?

An even better antifreeze than alcohol is ethylene glycol. If half the water is replaced with alcohol, the freezing point is lowered by 32° Celsius (57° Fahrenheit). If half the volume is ethylene glycol, the freezing point is lowered by 34° C (62° F).

Ethylene glycol

This small improvement in freezing point is not as important as two other features of ethylene glycol. It is not as flammable as alcohol, and it raises the boiling point of water, so the car doesn’t boil over as easily as it would with water or alcohol and water.

If you live in a place where the temperature never drops below freezing, you don’t need antifreeze. But you might want to add ethylene glycol to your radiator water to raise the boiling point.

Commercial antifreeze also contains rust inhibitors (silicates, phosphates, and borates) to make the engine last longer. These control corrosion by keeping the liquid slightly alkaline. A green or red dye is also added so you can tell antifreeze from other liquids that might leak under your car. Orange-dyed antifreeze has rust inhibitors made from organic acids, which last longer.

Diethylene glycol

Another antifreeze ingredient is diethylene glycol, although usually in much smaller amounts, and sometimes only because it is an unwanted byproduct of ethylene glycol production.