Achim,
I would only use water in an evaporative cooling system. I have a one cylinder engine using an evaporative cooling systm. It runs just fine at the higher temp, but does consume a surprising amount of water. I use 30-70 mix of ethylene glycol in my Titan and if you are close to the running engine after about 10-15 minutes your nose will detect the sweetness of the glycol from the invisible cooler vapors. I then shut it down for awhile. EG is toxic. We had a woman kill two husbands in our area years ago using EG as a sweetener in their food and drink. Husband number 3 survived her attempts and she was convicted of murder. I would not use EG in an open cooling system unless you can keep the coolant temp below 130F.
Jeff