Mobil 1 10w-30 tri-synthetic in my Prairie 650. I have had very good luck with it in my vehicle. It is rated as an energy saving oil and I have read that that type of oil is not good for atv's with clutches.
I think it would be ok in this case because the 650 only has gears in the tranny since the belt and pullys act as the clutch.
Also does anyone know if the oil filters from the Prairie 400's are the same as the 650's.
Thanks in advance for any help....