my brother has '99 400EX and i noticed today when we were riding (i have a Banshee) that his oil was really thin, i mean REALLY thin. so we did an oil change and rode for another hour or so and checked his oil and it was thin again. the oil didnt smell like gas. any ideas??? ~Rootman

What weight oil are you using? I use 10w40 and it thins out really fast also. everyone I talk to says to use 20w50, so thats what I'm switching to next oil change.

Yeah Im using 10W40. that is what the book recomended. you said yours thins out quickly but in an hour?? thanks for your reply. ~Rootman

Depends on how I drive it for that hour. If I'm just puttering around its not to bad, but if I drive it like theres no tommorow which I usually do then yes it thins really fast and I mean thin like water. My friends is the same way. hopefully a heavier oil will help.

I'M an avid ATV racer. I'm sponsored by my local HONDA dealer. He recommends that I use 20w - 50. Haven't had a problem with mine thinning yet!!!