Well, I have a Onan 15KW MDJF converted to radiator cooling on a trailer, that gets used for standby power during outages. It has been known to run at NO LOAD for 7 days straight. That's 168 hours. It regularly runs for 24 hours a day and is very lightly loaded for maybe 8 of those hours. Mostly it keeps the computer running in my Brother in laws office when the power is out. The oil is always clean and clear. No smoke, starts instantly,no problems whatsoever. But then it only had about 5000 hours on it when we converted it, and we've maybe used it another 1000 hours,It gets loaned out amongst family a lot, and there is a 225 Lincoln welder and a cutting torch on the trailer so its kinda popular. When used for welding the power draw is sporadic at best, maybe 90% no load then a small load for awhile. I expect that it will only last maybe another 10,000 hours. Running with no load is tuff on them.