Ramble,
Thanks for posting your OA results... Double thanks for having more than one reference point by providing two results. Triple thanks for doing a generator.
Spent several hours mulling the results and what they may or may not mean to me.
It seems odd that a Mobil product would shear out of specification. If I understand your data, the oil was sampled in 2014 but was installed about 28 months before. Sometime in late 2012? It is possible that being of that vintage, there was something a bit different in the formulation due to it's manufacture date, SAE requirements OR because it was a High Mileage oil. Still, to shear out raises questions. But, I suspect that there are millions of engines of all stripes running billions of hours on slightly out of spec. oil.
That said, some oils do start as a '40' or '30' for example and with use do shear down to a 'light 40 or heavy 30'. You get the idea. Nevertheless, it doesn't look like any harm has been done based on the results of the second OA.
IME, having performed OAs on my different vehicles (using different oils over the years) I have found that Mobil products tend toward increased iron levels. Don't know why, but there's tons of iron in an engine so it's of no consequence unless it goes off the charts. Just saying, high Fe is typical of Mobil products in my experience.
Using a XERO W40 doesn't appear to have caused any harm at this point. But, it is 'early' with only 40 some hours of use. While I use 0W20/30 oils here in Texas and now 5W30 in the Sprinter diesel, their low cold viscosity is rather meaningless in a climate that rarely dips to 32.... maybe sometimes into the teens. But these are water cooled gassers. A 5W20/30 would work just as well.
Air cooled jobs may require a bit more thought. After looking at the oil requirements for my Onans over the years, I settled on the OEM recommendation of 15W40 OnaMax. My reasoning is this: 15W will take me down to about 15F (-10C) that is good enough for my purpose. I'm not going RVing in sub-freezing weather. Likely, not even in near freezing weather!!! On the other hand, at oil temperatures below 100C (~212F) the oil does not achieve its 'summer' weight of 40. So, the multi-vis 15W40 should provide low temperature start up; less viscosity as it warms to 100C; and then stabilize around the necessary 40 weight when it's cooking. So, for me, going to protective levels below those where you routinely use the generator doesn't seem to have any positive effects. Neither does it appear, based on your OA, to have any negative effect at low engine hours.
I don't think a 0W/5W provides any warm up ability due to its thinner viscosity. How fast the oil warms up depends on how much heat you are putting into to the oil; how quick you are doing that heating; and the quantity of oil you are heating. An Onan with 1.5L capacity will warm up a hell of a lot faster than my Sprinter diesel with 12.5 L in the crank case. Thinner oil would not seem to make a significant difference in warm up with such a small motor.
Another factor I considered is the location of my generators: under the RV, in a box, inside a box, behind the rear duals. On a Texas day, the road temps are amazingly hot and more so behind and under a working RV. It's going to be hotter than the hubs on a hell wagon inside the Onan box, inside the compartment, under the RV. So, at least a 40 for sufficient protection all year round.
Thanks for the OAs. Good work!
