some points
2006, sportsman 800
2400km
good compression
no leaks
no loss of power
no smoke
no oil on air filter

now i mean its loosing a ton of oil! full to add in 20km ride.
zero smoke. doesnt sound weird. power seems just fine.
this is bugging the hell out of me.
could it be piston rings? but that would cause smoke?
valve seals? also would expect to see smoke.
even if it was leaking somewhere and i just couldnt see it i would expect a pool of oil to be under it in my garage, but nothing shows up.

im out of ideas. and need some help!
tahnks!

 

From what I experienced 800s did use oil as they got older.. Several have come into the shop for general service and I've found them to be low on oil. No complaints from the owners either. As to the exact cause? Could be rings,leaking through the valve guides,etc. You're not the only one that has had this happen. A simple search shows several complaints on this. https://www.google.com/search?q=spor...utf-8&oe=utf-8 As long as it's running good,no smoking or leaking,I'd just keep a check on the oil level and keep it topped off. Better than tearing into it without being able to pin point the cause. Rzrs had a similar problem,but in their case it was ring wear from dirty,neglected air filters for the most part. See if this video might help also that some have found.

 

Thank you. Is there an easy way to diagnose if the oil presure releif valve is the problem?

 

You gotta pull the plug and visually check that the relieve valve"bullet" as I called them will pull up with a magnet and not stuck. May or may not be your problem,but good to check it out for any wear or galling. Remember the way it went in if you remove it. My two cents I just think these engines rings just wear down quick in these plated cylinders,maybe they're too soft. That's about the only real explanation I can think of as many have had the same problem on using oil,but no smoking or leaks.Oil has to be going somewhere and the only possible place is through the tail pipe mixed with fuel?