EXTENSIVE black soot

My '84 300D Turbo emits alot more black soot than other 300D Turbos, as when I accelerate, most noticably at night time, I can see that clouds and clouds of thick black soot shoot out of my car, nearly blacking out headlights in my rearview mirror as the clouds hover into traffic behind me; im wondering if somthings wrong. I drive on average 50 miles a day, and use redline diesel fuel catalyst every thousand miles.
I have noticed that I also strangely dont have to add oil into my car as often as you would expect, maybe every 2 thousand miles I add a fourth of a quart of oil. Is this odd?