Since you do not know what kind of coolant you have in your 912, I suggest that you drain all of the existing coolant out and thoroughly flush the system. If it was EVANs, I recall that there is a procedure suggested to totally purge the EVANs from the system -- you do not want to mix EVANs and water.
Apparently, ROTAX has removed EVANs from it's list of approved coolants -- particularly for engines with the new cylinder head design. Everything I have seen including the RV-12 Maintenance Manual suggests Prestone Dex-Cool 50/50 coolant (pink in color) which is what I use in my 912.