In most heat transfer applications ethylene glycol-based fluids are your best choice because of their superior heat transfer efficiency. This efficiency is largely due to the lower viscosity of ethylene glycol solutions. Another benefit of this viscosity advantage is lower power consumption for re-circulation pumps and a lower minimum operating temperature
Propylene glycols are most commonly used in applications in which low acute oral toxicity is required, or for freeze protection where incidental contact with drinking water is possible. In some areas, use of propylene glycols is required by local regulation. Propylene glycol-based fluids are used extensively in food processing applications, but ethylene glycol-based fluids can also be used in some instances
I have always used 50/50 EG and water for engine cooling water systems. I was caught a little off guard when someone asked if the radiators needed to have a containment basin. I have never seen one around a radiator. It only holds about 100 gallons and the entire system only holds about 300 gallons. I believe the reporting requirement for a spill is 5000 pounds, which would be 550 gallons. In addition, it is unclear to me if that is for pure EG or mixtures of EG and water.
