RossKean
Well-known member
It isn't inadvisable to use a 5W in warmer temperatures, it just isn't necessary. It isn't "too thin" when temperatures are warmer - a 5W40 won't ever be less viscous than a straight 40 weight oil at any temperature. I think that in the earlier days of multigrade oils, viscosity breakdown was a bigger deal than it is today so perhaps a 5W would thin out sooner than a 10W or 15W? (Wild-*** guess) Not an issue with modern multigrade synthetic oils.That's the difference. I don't ride anywhere that it gets cold enough to allow 5w to be advisable. I'm more of spending most of the time needing 15w50.
Where I live, the bike is off the road for most of four months (WINTER) and there may be another month when I might be riding at 10°C (50°F) or a bit lower when starting off in the morning. I prefer the 5W under those circumstances because it will flow faster in the time before the engine warms up. Once the engine is warm, it doesn't matter. To be honest, I would have no qualms about using the (relatively newly available) synthetic Rotella T6 15W40. I don't ride very often at temperatures where the lighter grade is really needed. I haven't up until now because it wasn't available in my region (the conventional T4 15W40 has always been available, but not the T6).
I would note that many car manufacturers are recommending 0W20 oils, even in markets with higher average ambient temperatures.
Just because of Yamaha's recommendation, I would shy away from a xxW30. Probably OK, but why chance it?