Change fuel filters before or after diesel purge?
 

So I am in the process of changing out filters and fluids on my recently aquired 75 w115 300D and will be changing out the fuel filters next. I also plan on doing a diesel purge at some point. Which should I do first or does it not matter? Thanks.

After.

after , in that way clean fuel is moving into the purge process so one less area for contaminants. Plus no fuel or gunk should flow back into the filters

Before AND after! This will ensure you have a good flow of the purge through the system without any obstruction by the old filter.

Anytime I'm servicing diesel fuel systems (&/or working on performance/drivability issues) I like to replace the little plastic filter first, then test. Many times I have been pleasantly suprised to find that fixes the issue. The plastic filter is just a couple of bucks, and replacement certainly does no harm. If you replace it before doing a 'diesel purge' I think you'll find that it traps a lot of junk so buy two or three. Mike D has the correct idea. Before & after is a good idea, at least for the small filter.

I have always done this before and after. You are dealing with a lot of unknowns so it is best to be ready for the worst.

And if you find you don't need the few extra filters? Put them on the shelf and use them later. They will last 40 years as long as they stay dry.