I picked up 250 dirt bike to play with. It's a 4 stroke & air cooled.
Lots of guys on the dirt bike forums suggest Rotella T6, 5w40.
Book calls for 10w40
Being in the South, 5w40 seems thin. Also, the T6 is listed as a diesel oil and has "some" friction modifiers, bad for wet clutch.
So why do so many guys swear by it?
It's partly because of the cost as these bikes require frequent oil changes, but they only hold a hair more than a quart!
Thinking of just sticking to the Mobil1 4T I use in the Gixxer @ $10 at

Any knowledge out there about single cylinder, air cooled 4 stroke thumpers?

Welp, 2 things. What year is the bike? And how far south? Air cooled, I'm gonna assume (I know, I know) that it's at least from the early 80's. Plus hot weather? I would run the Rotella 15-40 in it. Both the 15-40 ( I believe it's the T-5), and the T-6, 5-40 are rated JASO, which means it is indeed wet clutch safe. If it's old, and you get hot, I recommend a thicker than stock oil. Not thinner. I have been running the 15-40 in my '83 GS 750 for over 10 years. Good stuff, and quite a bit cheaper.

South as in Alabama. Actually 36* last night, but usually warmer. Summers are hot.
2020 Kawasaki KLX230R.

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