I just double-checked and there is no oil leaking from the drain plug (or anywhere else visible) with the generator running under half load for ~6 minutes.
Here is a 34 second video I shot of the generator running under half-load. I noticed no additional leaking from the crankcase(?) bolts while running the generator just now.
It's hard to tell, as I don't usually spend much time inhaling generator fumes (or even running it beyond a few hours per month), but the exhaust fumes might smell stronger / a bit different. No obvious coloration or visible exhaust smoke, though. Generator has 700 hours on it, ~650 of which are from the previous owner. I'm not sure that he did the regular oil changes he claimed, seeing as the oil I drained (it's supposedly been a year, and ~50 hours of runtime) was jet black. The generator starts fine.
I'm out in the wilderness now but will be heading into town tomorrow and will pick up 15W-40 dino oil, swapping it out this weekend unless a better idea / explanation comes through.
*That said, I have found plenty of threads where people have had no problems switching to synthetics and wonder how that could be a cause of my oil consumption issue.
Just found this quote in an old thread:
"I worked for Cummins Onan between the years of 1992 through 1999 as a Level III certified technician on Industrial products and Level II RV. Never heard or read where the use of synthetic oil would affect the warranty. Saw more problems with folks not changing oil, not using the machine, stale fuel and a whole lot of other issues. Never an engine failure due to synthetic oil and never a question if synthetic was or was not used."
This thread seems to have knowledgeable oil discussion and recommends the same viscosity Mobil 1 synthetic I used. Hmm...
