The lubricity additives are added by a third party. As far as the motor oil, over time there is a lot less blow by getting in the chamber than if you are adding oil to the diesel. Oil blow by will cake up the combustion chamber. I know because i run and rebuild fuel testing engines so why would you add something that will foul it up? You can do whatever you want to your fuel. Lubricity additives are put in to make up for the loss of sulfur. Motor oil has minimum levels of sulfur. But just saying why would you put something in the fuel that is not supposed to be there. And no, I'm not saying that because the "evil" oil company tells me.