95.011: Propylene Glycol vs. Ethylene Glycol Antifreeze


From time to time the Tech Service Department receives requests for information on the freeze points and boiling points of various dilutions or Ethylene and Propylene Glycol coolants.


The generally recommended and most common practice in the use of glycol based antifreezes is to use 50 vol% water and 50 vol% antifreeze The water should be pure water, such as deionized or distilled water.

In some instances, a fleet may desire to run a weaker (more water) coolant to improve heat exchange and/or reduce antifreeze expense. This practice results in reduced corrosion inhibitor concentration, poorer freeze protection and slightly lower boiling points. The inhibitors can be fortified using additives such as Pencool® 3000. The boiling point reduction may result in undetected coolant boiling, since many engine temperature warning devices are set at 260°F, and weak coolants will boil before they reach this temperature.

Freeze protection, as the graphs illustrate, show that maximum protection is achieved with Ethylene Glycol Coolants at 67% antifreeze and Propylene Glycol coolants at 100% antifreeze. Customers are strongly advised to consult with their vehicle and/or engine manufacturer before exceeding 67% glycol concentrations. Heat exchange properties are significantly different at higher concentrations. Ethylene Glycol concentrations above 67% are counterproductive and are not recommended. The following graphs offer useful information.

Boiling Chart