Sure you wouldn't know everything chemically through fleet maintenance, but, it is a good tool in any type of equipment regardless of the usage which you are well aware of. I am just trying to pick your brain Pkruse, thats all. From what you have done mentioned in your posts obviously shows that if our oil is kept clean from all contaminants we encounter not only does the base oil stay in good condition but the V.I. do as well.
If you run an engine harder, then you have to change the oil or filter more often. For that reason, some OEM's offer an alternate to changing by miles. They offer maintenance by total fuel consumption. The Canadian coast guard idles their rescue boats all winter to keep them ready for a call. Their schedule might call for a filter change every 6000 gallons, for example. So if they get a lot of rescue calls, they would be changing it more often. If they install a better filter, then it is even less often.