Primary filter is the in-line filter
Secondary filter is the spin-on filter

I changed mine at 8K+ mile as I have a washable diesel water filter prior to primary filter. It is desirable to pop test the injector at a fixed interval but it depends on who you talk to.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

I believe that the fuel filters are a 36,000 mile item on the 603 maintenance chart.

__________________

Gone to the dark side

- Jeff