Sidecarflip, do you use 10w30 or 15w40?
I used to run 15-40 Rotella but I switched to 5-40 T6 about 6 years ago and have stuck with that because the 5-40 lets the engines turn over easier when cold. Remember, I don't have block heaters on them nor do I have electricity in the barn so they sit in ambient temperature in the winter. Same with my pickup truck.
Candidly, I was amazed how clean the overhead was and I took my finger and ran it over the topside of the head between the valve mechanism to see if there was any sludge laying on that surface and there was none. Just as clean as when the engine was new.
Last summer I replaced the HUEI and glow plug harness on my 1997 7.3 Navistar in the pickup which entails pulling the valve covers and same deal, clean as a whistle underneath. You could plainly see the paint marks on the valve springs and the catalog numbers on the injectors and the valve covers had absolutely no blowby residue on the underside. Didn't even wipe them down. Just reinstalled them.
My pickup is the same deal. Oil colors a bit between changes but never gets black.
The valve clearance is excessive on the M9 and I expected that. I'm way past Kubota's recommended valve adjustment interval. WSM says 0.008 -0.010. Told Dennis to set them towards the 0.008 side in as much as I don't run that particular tractor that hard, it's a rake tractor.
I still believe the black oil at drain time is caused by the pollution controls and carbon getting in the lube oil.
With 4000 meter hours on the M9 engine, I expected some blowby and dirty oil from that and that hasn't happened either. Hardly any vapor comes out the road draft tube from the valve cover. Remember, this motor is not a pollution motor, no emissions hardware / software whatsoever. and...
I always use Powerservice in all of them, all the time. Winter = red, summer = white.
Must be doing something right, think I'll keep on my program exactly.