Should I change the fuel-water seperator when I change the fuel filter?

I dont. I carry a spare and change it when it gets close to the change line or the 3rd oil change.

 

What gauge are you reading?
I traced my fuel filter restriction gauge line from the dash and it seemed to terminate at the primary filter housing. I have a 97 379 w/ 550 cat. Because of that I would just change both filters when the restriction gauge would climb a bit, usually between 15 to 20k.

 

Fuel filter restriction gauge. Yours hooks up same place mine does. When mine gets over 15 I change the FWS then it generally drops down to about 2, when it doesn’t drop down to below 5 then I change the secondary filter. I can’t say it’s wrong to change both all the time I just don’t want to waste my money.

 

I understand now, I thought the restriction gauge read only the primary filter where it was hooked up, my mistake. Guess I'll start changing the filters how you do it.

 

I've had this truck since 2003 and had that happen twice. Once was a tan sort of blob about the size of a nickel. The second was a sliver of black rubber the size of a quarter. At that point I suspected the inside of the fuel line from the tanks might be deteriorating so I replaced all the fuel lines.

 

Absolutely change both. Cheapest insurance there is.

 

Being risk adverse myself I would change both. Filters are a lot cheaper and less time consuming than fixing a resultant problem later.

 

Hi guys. I change my primary cat advanced filter every 5k when the filter is holding to much water, probably due to the fuel station I go to. And again at 10k with the secondary at my regular total service. I’ve noticed that my my split tank is black on the inside, most likely algae. I was using Killem from FPPF and a mechanic friend told me not to use it, does more harm than good. Anything on the market that I can use to eliminate the algae in the tank