Heat Transfer Properties of Engine Coolants

Water is a much better heat transfer fluid than ethylene glycol or propylene glycol.

Engine coolant's primary job is to transfer excess heat from the engine to the environment.

The engine cooling system is engineered to take advantage of water as the primary heat transfer fluid. Water is assigned a heat transfer value, specific heat, of 1.0.

Other fluids are compared to water. Higher vales transfer heat more poorly, while vales of less than 1.0 would transfer heat more efficiently. Ethylene glycol has a specific heat of 2.78, and propylene glycol has a specific heat of 2.73. At 50% water and 50% antifreeze, the specific heat of engine coolant is much closer to that of water.

This illustrates the necessity of mixing water and antifreeze to make engine coolant!

In very warm areas some operators use water with corrosion inhibitors. The use of water is successful because although the boiling point is lower than with glycol-based antifreezes, the heat transfer is better, and the operating temperature of the engine often decreases enough to avoid boil-over problems.