With a 50/50 mix of
antifreeze and a 15 psi pressure cap, you won't get boil-over until about 235 F. If your winter temperature doesn't get below 0 F, you should be able to get by with about 35% anti-freeze and still have a boiling point of 230 F. Water is a better heat transfer agent than
antifreeze or an
antifreeze mix, and much better than those "waterless" agents. With the latter, your engine will probably run at 220 F instead of your current 200. If you're peaking at less than 230 F, I would just add the water wetter and not worry.
