Duramax smoking

Few week ago in town I saw a pick-up truck (diesel, but don't know what brand it was). The owner modified the exhaust so it came out the bed of the truck with 2 pipes that were higher than the cab. Really a show off. It was belching black smoke like an old freight train. I've been told if you mix oil with the diesel it will make the smoke black. I was really irritated by the smoke. I do remember the day when diesels did belch black, especially the semi's. I think anyone who does this is a pure idiot. But leaking oil is another matter. That's not a deliberate attempt to show how much of an idiot one is.

Hope the guy you referenced to above can get it fixed.