Hey Tom , my wifey's Toyota Corrola lists a 5 -30 wt oil year around ... I asked the guys at the dealership and they told me that the reason the Japanese engines need a lower viscosity oil was because of the close tolerances of the lower end and the improved designed oil lubrication system in these engines ... you never see a Metric Bike for sale ad that says rebuilt lower end and top end .... these Japanese engineers have these engines down to a science , man
.... as far as your question Tom , maybe it might have something to do with where you live at if its a cool climate than the rest of us in the south ... just an idea ... Thanks the Geezer
