As most are aware, the engine oil specified by Aprilia for the Rotax V990 engines fitted to the Falco and Gen1 Mille & Tuono is:
- Semi-synthetic SAE 15W - 50
- 10w40 JASO MA
People often discuss the merits and demerits of using Fully Synthetic oil in their V990 Rotax.
Certainly, from the reports, it seems that fully synthetic oil makes clutches that are prone to slipping even more susceptible. You probably don't want to entertain the idea on the old bikes (especially the Crow Black and Fire Red Falcos).
So why might you consider a fully synthetic 15w50?
Although I'm not suggesting that you should switch to a fully synthetic oil, the following information makes interesting reading. I have not been able to confirm its accuracy but it is certainly food for thought.
Aprilia's Bulletin for those having trouble with clutch slipCETME from AF1 forum wrote:Well,
Initially, as we all know, we had single conventional grade oils, such as 30, 40, 50, etc weights.
The problem with these oils, as you can imagine, is that they have poor cold weather properties. Viscosity is the thickness of the oil, and is the inverse of temperature. The warmer the oil gets, the thinner it gets. The colder it gets, the thicker, or more viscous it gets.
So multi-grade oils were invented. A 10w30 conventional oil is a 10 weight base stock. A straight 10 weight oil is much thinner at 100 degrees than a straight 30 weight. So Viscosity Improvers are added (VI's.) VI's are basically polymer compounds that expand when heated. This prevents the 10 weight oil from thinning so much. It allows this 10 weight oil to ACT like a 30 weight oil would at temperature. This allows the benefit of a 10 weight oil during colder temperatures, and startup, yet have the benefit of a 30 weight once at operating temperature. Keep in mind that oil always thins as temperature goes up, but the rate at which it thins can be controlled by VI's.
VI's though, are not perfect. They degrade rather quickly, especially in high heat, or high stress situations, such as turbo chargers or motorcycle transmissions, where the gears smash the oil. The degradation of the VI's is called oil shear. This means that a 10w30 is more stable and longer lasting than a 5w30 because it has less VI's in it, since it already starts off as a heavier oil. After only a thousand miles or two, your 5w30 in your truck is probably around a 5w20, and will eventually get down to a straight 5 weight if you leave it in there too long.
10w40's and 5w30's are particularly prone to this problem, because they require quite a large amount of VI's to function. If you put 10w40 in your truck, consider using a good diesel truck oil like a 15w40 Rotella that is much, much more stable than the passenger car 10w40, in addition to having a much better additive package that prevents wear in the engine. This additive package, however produces SLIGHTLY more emissions, so they are phased out of car oils, but the "Diesel" oils still have them.
Now thats out of the way, lets go onto synthetics. I don't want to get off on too much of a tangent, but not all synthetics are equal. Some synthetics, like some of the valvolines and pennzoils are not real synthetics, but merely a highly refined conventional oil that the government allows to be classified as synthetic. This is still a group III oil (conventional) and not a group IV oil (full synthetic.)
Anyways, a full synthetic is less affected by temperature than a conventional oil, by a HUGE margin. In a 10w50 or a 15w50 (it really doesn't matter) they simply take a synthetic base stock of straight 50 weight oil and essentially do nothing to it. Because it remains thin at cold temperatures and resists thinning at higher temperatures they don't have to start off with a thin oil and then add VI's to it.
This also means that because there are little to no VI's in synthetic oil, it is much more stable and longer lasting than a multi-grade conventional oil.
The fact that a Xw50 synthetic can pour down to -39 degrees, while a 5w20 pennzoil can only pour down to -33 degree is pretty amazing. It also tells you that a straight 50 weight synthetic is liquid at -33 degrees while the 5 weight conventional turned into a gel.
So that is why the first number does not matter in a FULLY SYNTHETIC oil. Because its really just a straight weight oil. The general public would have a hard time getting their minds off multi-grade oil numbers so the oil manufacturers put the first number on there to confuse people less. They simply put any old number at the front that most people would be comfortable with, or they think they would prefer, but its pretty much all the same.
