So in my haste to reply I forgot some important information. Some may remember that a number of years ago Rotax published a list of oils that were suitable for out dry sump engines. This however was affected by changes in the worldwide desire to remove heavy metals in fuels and OILS used in engines. The standard protector used in oils for our design type was oils that high levels of ZDDP, basically zinc and phoshopis with carriers. The old standards for auto fuels were about 1200 PPM of these and were good to protect your flat tappet lifters and camshafts. It also did a good job to protect the gearset. Regulations within the automotive industry and high volume motorcycles pushed oil companies to reformulate and drop these down to about 800 PPM. The result was a disaster for flat tappet engines and most automotive engine suppliers had to switch from flat tappet to roller lifters. For the most part internal gears were not metal in these engines so gear protection was not much of a problem. Rotax users discovered major problems with some of the reformulated oils. A few that had been very popular were Motul 5100 and Catrol GPX, these has worked very well however...the reforumated versions were a disaster. At issue was how they worked with the Rotax dry sump system. They would foam.
In testing we discovered that these particular oils would hide inside the crankcase, stuck inside the block as foam bubbles. Up to 1 liter of oil would stick to the walls and if the oil tank was not full it could even unport the oil pickup tube. In answer to these oil changes both the Motul and the Castol were on the bad list...do not use. Given there are literally hundreds, indeed perhaps thousands, of oils to test this pushed Rotax to start to work with Shell for the first branded oil. The incident response was a change in the dipstick, yes the dipstick was changed from a round top to a square top. The difference was in increase in the oil level to its maximum so that low oil from foam would be less likly to unport the pickup tube inside the tank. This was a major mandatory change for all engines at the time.
The bottom line here is to remember just because an oil may meet the written requirements there are also things going on that we have to be wary of. The foam issue turned out to be a slight reformulation change of adding too much silicone to the blend. If correct amounts it will prevent foaming, in the way the Rotax dry sump worked it did the worst thing by foaming excessively.
One last item. Oils from motorcycle racing are considered as boutique oils, as such they are exempt from the standards that dictate how much zinc is inside. Mobile MX4T has very high zinc, about 1700 PPM. An odd effect of this some find disturbing in that an engine using this runs fine but will always have a lot of black ash deposits on the top of the piston and in the combustion chamber. The lifters and cam and gears are great but the very high levels of zinc burn and an ash deposit is left behind. Not that I have seen any issue with it but it is worth noting. So in my opinion oils at 800 are way too low, 1200 is a sweet spot and more than that is fine but I don't think we need it. Just my opinion.
One last thought. Check your oil supplier hazmat data sheets. Valvoline used to make a great oil in the EU, it was highly respected and worked great. When customer started to use it in the USA we had major problem. The exact same oil label and description was used in the sales material but the oil in the USA was blended differently. The USA oil had a friction modifier that would allow the clutch at high loads to slip. it took some searching but the problem was the formula change from the European oil to the USA blended oil. Another fail from the oil company.
Lots of luck with oils, be skeptical of what they are selling you and do your homework.
Cheers
