20w40 or 10w40?

Have an '02 R1... am wanting to switch to Amsoil. Local dealer has 10w40 MCF in stock for other sportbikes in area, but looking in service manual it says to use 20w40 for temps 40 F and above. Will using 10w40 cause and damage?.... Called local Yamaha service dept and they said to use 20w40, could be problems if not.... I have been using Mobile1... can't remember what weight, for a few years, never seemed to have any problem... this same dealer said that using Mobile1 could damage seals and cause leaks.... true?

Have an '02 R1... am wanting to switch to Amsoil. Local dealer has 10w40 MCF in stock for other sportbikes in area, but looking in service manual it says to use 20w40 for temps 40 F and above. Will using 10w40 cause and damage?.... Called local Yamaha service dept and they said to use 20w40, could be problems if not.... I have been using Mobile1... can't remember what weight, for a few years, never seemed to have any problem... this same dealer said that using Mobile1 could damage seals and cause leaks.... true? The reason that Yamaha is recommending a 20w 40 is because they sell it and it is not that readily available from anyone else. This is mostly marketing to get in your wallet. The other statements they made about other oils is just their way to place doubt in your mind so you will give them your business. In your case the 40 weight is the key as the bottom number is for cold weather operation. george ADG

I use amsoil and so do all my friends (1000rr,R6, R1 all 2007) 10w40 and have had no problems, in fact the bike runs better (shifts with ease) and cooler. Love it. Its also affordable, go to their website and become a preferred member. Shouldn't be more then $100 bucks shipped for a box of 12 quarts

Or, click on our Banner Ad here and support a Forum Sponsor. Any Dealer in our Group can set anyone up as a Preferred Customer and then you also have Personal Contact with someone. Bob S ADG .

mobil 1 20/50 in all my cars and bikes