Hi All - Rotax used recommend Castrol Anti-Freeze Anti- Boil Concentrate at 50:50 . Rotax viewed this concentrate as being a formulation "low in silicate and free of nitrate". I have run out of the supply that I had on hand and now find that the above product is not being stocked by my supplier. Questions; 1. What is the name of the current Castrol substitute for the above? 2. What concentrate are most Rotax 912 drivers using? 3. I have access to a supply of reverse osmosis (RO) water - is this okay to use? 4. Or should I go out and purchase deionised water? 5. Or Distilled water?