There seems to be some confusion as to what coolant you can use for your liquid cooled Rotax. Rotax currently lists only fluids where they have had feedback from the countries Rotax distributor about what is available and what has worked. The list therefore is not always going to show your favorite brand and perhaps we need to look more at what are the best things to look for in a coolant. There is a lot of good information from the coolant suppliers in form of materials safety data sheets, MSDS, that will give you what you need to know. In general, most enough information is on the container, we have to take a few moments to look carefully at that information.
So what are we looking at with our cooling system? There is a ceramic seal directly behind the water pump impeller (yes even on the 2 strokes starting with the type 582) We also flow fluid from the radiator into an aluminium housing and impeller, into a rubber hose, to an aluminum head and out with a rubber hose again into a collector and back into the rubber hose to a radiator. We use a pressure cap with a coolant recovery ability and it should use a coolant recovery bottle. We can look at the failure points after.
Historically the way liquid cooling worked on the Rotax was to treat it like your car. We would use some diluted ethylene glycol mixed with distilled water. This prevents freezing and the whole system is under pressure to raise the boiling point. In 1989 when the 912 came online early engines all used mostly the same coolants. They had additives to keep the system clean and prevent corrosion internally. The most common ones used silicates, older fluids used phosphates. Coolants with phosphates however cause a great deal of corrosion when flowing in an engine with a lot of aluminium so it was not a good match. The term " aluminum compatible" was used with fluids where the phosphates were removed, silicates were used to take up that task. The fluids themselves were what we now term inorganic additive technology, IAT. For the most part other than the number of additives the base will hold the silicates in solution for a period. (generally, no more than 24 months) These fluids however had some issues. The IAT fluids can break down and release the silicates, they will separate at some point. As the fluid ages it also becomes more electrically active. This can produce, with the flowing fluids, electrical-chemical discharge. The phenomena is called ECD. You can measure the flowing fluids with the IAT types electrical current when the engine is running with a multimeter. It was not uncommon to see water pump seal failure due to contamination from the silicate drop out after as little as 500 hours with those coolants. Since many people don't want to believe someone without a name let us just go to a coolant manufacturer ad see what they can tell us. The link has nice short explanations of each type of fluid. I can tell you that any good OAT or HOAT coolant is far better than the old IAT versions. (my view) But for sure never mix between the blends or type of coolants.
https://www.valvolineglobal.com/en-eur/all-you-need-to-know-about-coolants/#.
Cheers
note, also check out gates hose web pages for information on hose replacement requirements from a hose manufacturer
