“What do you mean, it’s not for used motor oil?”
I’ve been saving my used motor oil for my sub-compact, mechanical injected diesel tractor. 85/15 used oil/gasoline is a thing and guys have used it in their moderns diesel truck engines. There is some big time filtering of the used oil required. It was invented/concocted by someone during the Obama admin when diesel was approaching $5.00/gal.