well, the clear filter is the primary filter in that the fuel reaches it first in the line. But i figure the big spin on one is the main because it is the most important. The clear one really isnt necessary other than to filter out the biggest particles and to get an idea of how clean your fuel is. Ive never seen any engine other than a mercedes diesel with a coarse mesh pre-filter like these have.

anyway, i think mine was last changed about 3 years ago, about 35k miles. I guess thats alot. It makes a huge difference, even compared to before i filled up with b90. so i think it should be at least an every second oil change thing, at least thats what im gunna do from now on.

__________________
1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350