The Rotax Installation Manual is quite specific about the acceptable types of coolant. I chose to use a conventional coolant based on ethylene glycol as opposed to waterless based on propylene glycol. Specifically I chose to use Prestone 50/50 Dexcool, one of the ones listed in the Service Instruction (SI-912-016). The engine itself only takes about 1.5 litres to fill, but you need to also fill all the hoses, the radiator, the overflow bottle, and the cabin heater. For me this took almost 4 litres in total. After the fill, things looked good at first, but the next day I found the overflow bottle was empty and there was a puddle of orange liquid in the hull. Not finding any obvious leaks I refilled the system and let it stand another day. Same thing happened. With the help of another set of eyes from a friend I eventually found a dripper leak on a connection at the cabin heater. So I re-tightened all hoses connections and filled for the last time. Good to go?
