Propylene Glycol I believe is used in a lot of "coolant" + additives for anti-corrosion etc.
It's freezing point when mixed with water is fairly important depending not least on where you live.
http://www.engineeringtoolbox.com/pr...col-d_363.html
And distilled or at least deionised water. Tap water will leave behind the salts/minerals when it evaporates, forming white dusting or even blockages eventually.
Out of interest, used to be Ethanol Glycol but it's poisonous and bad for the cute furry animals. This is why "anti-freeze" has such a bad rep for being drunk... in more ways than one.
Propylene Glycol can be found in candy, deserts, car radiators, club fog machines and electronic cigarettes.