My 85 only has 165K on it. The oil is black 500 miles after I change it. I don't even give it a second thought.

I have tiki torches in my backyard that I fill with diesel fuel. They put out a TON of black smoke, but I don't care. A gallon of diesel is what, $2.35? A quart of torch fuel is 8 bucks. I figure that dirty oil is just what you get when you drive a diesel.

My car only smokes during full throttle acceleration. The rest of the time you don't see a thing.