Per Can Am, use a 50/50 mix of an aluminum engine compatible antifreeze to distilled water.
Undiluted glycol based antifreeze will freeze at about -9 deg F, but a 50/50 solution can go to -35 deg F before freezing (apparently the two fluids inhibit each other's atoms from hard bonding at low temperatures). On the other end, pure water has a higher specific heat than a pure glycol based coolant meaning water will absorb more heat without raising its temperature even though a pure glycol based coolant will boil at a much higher temperature. So, the same 50/50 mixture in a 15psi pressurized system is a good compromise as it will go to around 265 deg F before boiling while pure water at the same pressure would boil at about 250 deg F.
All this and much more can be found on heat transfer fluid manufacturer's web sites if you're interested.
