RambleOnNW,
I commend you for having the oil tested. It's one of those things that I keep saying I'll do, but never get around to doing it.
Looking at the numbers, the 0W-40 definitely looks like there are more particles in it than the 10W-40, especially considering it was only in half as long. Do you know how many hours were put on the oil in each case? That would be important information as you could easily have put more hours on the generator in the 14 months than the 28 months.
Also, what weight oil does Onan recommend for your generator? On mine, I have found the recommended straight 30 weight works best unless we're camping in the winter, then I'll put a multiviscousity oil in it. Running the thinner oils during the summer, I have discovered that apparently the thinner oil sloshes around a bit more on hot days and the oil sensor will sometimes think the oil is low and shut the generator down if I hit a good bump. Haven't had the problem since using straight SAE 30.
~Rick
