Freezing Points of Engine Coolants

Pure antifreeze is not intended to be used without water

Most vehicles should be filled with 50% antifreeze and purified water.

Water is the heat transfer fluid, the antifreeze contains glycol and additives to offset the negative properties of water.

The curves below should be useful in understanding how various mixtures will behave at low temperatures.

Most engine manufacturers recommend that coolant contain from 40% to 60% antifreeze. The freeze point of pure EG antifreeze, interestingly is about -5 degrees F.

Engine Coolant Index (