Found this and thought i would share it, yamaha specialists are encouraging us to use 0w40
Randy Strickler
I agree that it is somewhat confusing that the owner’s manual tells you to use 0W-30 weight oil, but the dealer has some 0W-40 on the shelf. I checked with Yamaha’s lubricant specialist on this one to be very certain, and he confirmed that the full-synthetic 0W-40 can indeed be used in any of Yamaha’s four-stroke snowmobiles. In fact, he encouraged it. While the semi-synthetic 0W-30 is a very good oil, as you pointed out it has a cold pumpability specification down to -40 F. The full-synthetic 0W-40 will perform even better in cold conditions and has a cold pumpability specification of down to -60 F. That means whatever temperature it is outside when you go to start your sled, the full-synthetic will start flowing quicker and easier.
As an extra benefit, the full-synthetic is ester fortified, which is going to provide superior protection under high RPM conditions and high heat loads and is part of the reason the full-synthetic costs more. Ester has a little bit of polarity so it sticks to the metal parts. Another cool benefit is how when more pressure is applied to it, the more slippery it gets. The engine parts will stay very clean as this oil is very low in sulfated ash, so you won’t be seeing a bunch of sludge in the engine like with some other full-synthetic oils. This is the good stuff, and there is no better oil you can buy to protect your investment. This is what we use in our Yamaha four-strokes.
