My '78 240D is clogging up the fuel filters every 50 to 75 miles with a fine black substance. I have not run any bio-fuels in the car. Any ideas what this could be?

I have added an additional fuel filter before the primary filter so that I don't have to keep replacing the primary and secondary filters as often.

Thanks!

__________________
Chris Young

Current cars:
1978 240D 4-spd manual 99k miles
1987 300TD - 132k miles
1987 300SDL - 280k miles.
1996 Subaru Outback - 132k miles
2003 Chevy Silverado Duramax/Allison - 195k miles

"My wife thinks I have a disease..... I think I have just inhaled too much diesel exhaust .... My neighbors think, well, who cares what the neighbors think"