Our Cummins 6BTA (280HP) was spec'd for up to 250 hours between oil changes. That equates to 1,750nm at 7.5kt. On a continuous non-stop run there would be a need to add oil but not necessarily to change oil/filter. We did run non-stop for 7 days (168 hrs) without an oil change, though we usually changed at shorter intervals because we could and the engine was not running continuously
Exactly.
Manufacturers spec oil changes based on "normal" use. In 250 hours, that may mean a couple hours use each time. That equates to about 100 cold starts.
Cold starts are the key. That's when most engine wear happens, as well as oil contamination.
Back when dinosaurs roamed the planet, manufacturers used to not treat their customers like idiots. They would explain the range of use and have recommended frequencies based on that use.
BMW may still do that in their cars ghost tell you when it's time to change the oil.
At least in the 90's when they came out with that system, or was pretty much weighted to the amount of time the engine was running and still cold after start up.
If you did short city driving, 20 minutes at a time, you'd be changing the oil every few thousand miles. If you were commuting 200 miles a day, the change frequency was more like 10,000 miles.
Then just like that, the dinosaurs were extinct and were replaced by lawyers. I think it was around 1975.
For the last 20 years it's all lawyers and bean counters, sorry, accountants.
So in answer of the long forgotten question, I do believe I ran that little Ford Lehman 21 days straight this last time.
I did stop the engine the first time in the middle of the North Atlantic so we could go swimming in 14,000 foot deep water.
I'm not sure I'd do that again.
But I'm sure I'll never stop to change the damn oil. That's just cruising for a bruising.