It is still a good petroleum oil. It has a high level of dispersants for keeping the diesel blow-by in suspension 'til you drain it, and anti-foaming agents for diesel use. (and probably other stuff.) I just ran a batch of Rotella in my 225 before the change to Mobil 1 to clean things out a bit. The Mobil 1 solved my rod knock at start up, but I don't think the knock would have been any different with any other petroleum based oil vs Rotella. (Edit to add: I would only expect a full synthetic to do this, BTW...)
