Reading my nifty owner's manual for my Yamaha F70, it says to use the oil best suited for the temperatures in my area, and it gives me a nifty chart to look at.

That chart seems to say that 10W40 covers temps from about -15 to about 105F.

Whereas 10W-30 covers about -15 to about 95.

Since I'm in San Diego, (and live in east county), temps above 95 aren't out of the question.

So 10W40 seems superior to me. Covers more temperature ranges, including some at the high end that I might experience.

YET, all the oil change kits for the F70 come with 10W30. Even on Yamaha's site. And the only kits with 10W-40 are for PWCs.

Am I missing something?