We have diesels from 23 to 85 HP and stick with the regular maintenance schedules. Diesel oil gets black pretty quick; nature of the beast I guess. We change oil in the M8540 every three hundred hours.
Same here on my M8540.
If you really want to know where you are at on your oil, have it tested.
E/S
One thing I learned in the Navy is that oil doesn't wear out, the additives in it might get depleted though. Filters will get clogged and require replacement or cleaning, depending on the type of filter.
We used to get our hydraulic oil tested once a year, and renevated if needed (ran through a big set of filters for twenty four hours). Then retested.
Enginge oil in a diesel does get dicolored quickly.
Getting your oil tested is the best way, but it might be more cost effective to just change the oil and filter. I change the oil in my L175 once a year, in the spring. I usually put around 50 or 60 hours on it mowing my yard or moving trailers.
I figure that after it has sat all winter, I want to get any condensation out of the oil pan.
Robert