There is a vast amount of misinformation floating around concerning coolants, kind of like all the BS claims for so many other products on the market. Here are some actual facts.
-Plain water has better heat transfer properties than either ethylene glycol or propylene glycol.
-Ethylene glycol has a lower viscosity and higher thermal transfer than propylene glycol.
-Ethylene glycol has better freeze protection than propylene glycol.
-Propylene glycol is less toxic than ethylene glycol, thus it's use in "eco-friendly" coolants.
Advertisers of products like Engine Ice heavily imply their propylene glycol product makes your engine run cooler. However, if you look at the scientific data you see that the PG actually has a lower heat transfer coefficient than either EG or water. If you assume a lower water temp reading means your engine itself is running cooler, think again.
The real advantage of PG is the safety and environmental factors, not actual performance in a cooling system.
Jerry