Word is Yamaha believes the 10W40 is good below 40F and 20W50 for above 40F. They believe an oil pump wear issue may be related to using 20W40 as an all-season oil even in cold weather. This info would apply to Synth and Dino since Yami is making the change based on viscocity during warmup, and after warmup. There's no recall or anything, its apparently to make pumps live longer. BTW full Synth is now recommended to be 15W50 and can be all-season. This cold viscocity may help quiet your engine.
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