“From my experience (with Thielert, just for clarification), water cooling in aviation engines isn't that great. In summer, you have to make cruise climbs to avoid coolant temperature to go over the limit and in the winter you have to make very shallow descents - again to stay within the limits, whereas with conventional engine you have the advantage of manual mixture control to keep CHTs and their rate of change on a normal level.”
In 4.5 years of Rotax experience I have never had an issue with temps. Having said that I tend to cruse clime at 100kn and 1000fpm in preference max r of c as it gives much better forward vis. Tests have shown that in very hot weather at max r of c you can get quite hot if you go straight up to 8000 ft, but if you keep going to 10,000 it does not make much difference. Such a clime will start at about 1650 fpm, so 8000 ft does not take very long. Never had an issue in decent at all at normal speed. Most rotax installations have 2 X CGT, 2 X EGT, Oil t, Oil P, water T and volts so you have a good idea of what is going on.
Rod1