This discussion got me thinking back to my sailor days.
On the USS New York City (SSN 696) we ran 90 weight oil for the main engines and turbine generators. Let me see... if i recall about 750 gallons in the sumps for both 750 KW turbine generators and 3000 gallons in the propulsion lube oil sump serving the twin 15,000 HP main steam turbines and reduction gears. That amount once again in the lube oil storage tanks just in case we had to dump and refill everything.
On the boat, one of the nub nuke jobs every midwatch was running the three lube oil purifiers (and cleaning the SOB's) LOP's spun at about 3000 rpm and spun any water or impurities out of the oil (anybody here ever puked a purifier? nevermind). Then it went back in the tank. Oil never was changed unless we went into drydock for an overhaul. Now I know in an internal combustion engine there are some different chemical issues happening in oil, but it made me think back to the good ol' days on the sub, where the oil never went bad, it just got a little dirty.

Now I'm gonna have nightmares for a week.
Cheers
Josh