If you dont need the high freeze protection, Id opt for corrosion inhibitors in a solution of maybe 25-30% e-g in water (for some increase in boiling point), and a pressure cap of 22-25 psig.

        As noted earlier, all airplanes need freeze protection. I was flying recently in Tampa at night and the temperature at 15,000 ft was something like -10 Celsius.

        Water will often freeze in the radiator if you do not have anti-freeze, even if the engine is warm. The freeze will start in a low flow (water) region and will then spread as the flow is further blocked, perhaps bursting radiator tubes as it progresses.