First Hello to all.
I run a 3500 5th Gen Cummins
Do both fuel filters need to be changed every time I perform fuel filter maintenance?
I ask due to I change filters at 30/40% mark and both look in good/ very good condition when removed.
what effect would it have on priming, if any to only change rear fuel filter. Thanks in advance

 

You're think backwards, the rear filter is just a water separator strainer, so in theory as long as your water in fuel light is not on it should be just fine, the engine mounted filter is the one doing the work, it should be changed on interval, I'm getting 15k+ miles from the dash warning, i feel that's an acceptable time frame to just change both. Thats usually 2 oil changes.

You could look at the fleece kit that elminated the underbed filter and goes to a single spin on engine mounted filter, i plan on doing the swap one of these days