Standard green antifreeze is ethylene glycol and rust inhibitors. It should work fine at a 50:50 mixture with water. This ratio provides nearly the optimal ly low freeziing point and highest boiling point. (I think the actual optimal mixture is something like 56% ethylene glycol, but there is little difference in the freezing point supression and raising of the boiling point. So, the easy ratio to remember and make, 50:50, is used.)
