Use Full synthetic 0w-40 the oil pumps on the Polaris has tight tolerances and 0w flows oil to the motor alot quicker then 10w can on cold starts.
How can Polaris recommend, 10w-30 when they do not even offer it or sell it? They only sell 0w-40 in there single cylinder oil change kits since 1996. No wonder some people get premature cam wear. The new kits may be 2w-50 now but thats still closer to 0w-40 then 10w-30 is.
The OEM Polaris Oil change kit says " FOR ALL POLARIS FULL SIZE SINGLE CYLINDERS" so a guy with a 1996 Sportsman will buy the same oil and filter as a guy with a 2009 XP550 from a dealer.
I think Polaris did the 2w thing so people think they are stuck with buying oil from the dealer only, because 0W-40 was available from others while 2w-50 is not.
The 500 Fuji motor never changed since 1996 up till now except for a high duration cam introduced to the Scrambler in 98 and 2001 for the sportsman so they should use the same oil no matter what year the ATV is.
Polaris new oil is 2w-50, but 2w would still flow better on cold starts like 0w does. The first number( #w) is the cold start up viscosity rating for cold starts and the lower the number the thinner the oil,the last number is its viscosity at operating temperature, so on a warmed up motor 0w-40 is the same as 20w-40 but 20w would be like jello on cold starts compared to 0w.
Our 97 SP500 has nearly 8000 miles and has used 0w-40 Amsoil most of the time. We used many different oil filters on it but a Frame CPH6607 mostly just because it was available at Canadian tire.
Polaris still sells 0w-40