Diesel fuel & suspended dirt

[whizbyu]

I have a VW Mk7 TDI that I bought used as part of the VW DieselGate buy back, had 25000 miles on it, and I had it inspected before buying. I had my mechanic change out the fuel filter at the time of purchase. He eyeballed the canister and fuel tank and said the fuel looked fine. Now 15000 later, I decided to change out the filter. Upon removing the old filter I did not notice that the filter was all that dirty but it did have a slight yellowish ever so slight brownish discoloration. I've seen filters that are almost brown at times.
There was about a half liter of fuel left in the canister and I used a sterile irrigation syringe that we use in the operating room (this was clean and was to be thrown so I took it home) and aspirated the rest of the fuel, and poured it over a funnel that I lined with a cone type coffee filter. The first 200-300 ml's of fuel filtered through but I noted that the filtration slowed down considerably after that. In the end, the filter had a very faint/fine brownish deposit on it. The bottom of the canister also had that deposit and I wiped it off with a clean cotton cloth. The residue was fine like wet dust; nothing gritty. I put the new filter in, poured some diesel purge from LiquiMoly, and did a fuel pump prime with VCDS.
Question is, is diesel fuel supposed to be a little dirty? I am now tempted to change the fuel filter out more frequently; like with every oil change at 10K.
Advise appreciated.

 

[RooflessVW]

Diesel should be clean but can be dirty. My filter comes out clean at 20k.

I wouldn't do it more often; the filter is huge. That it was dirty means it is doing its job. 20k is a conservative interval IMHO.

 

[wwillson]

Diesel fuel is supposed to meet ISO cleanliness standard 14/13/11, but often gets dirt added during transport and distribution.

This is a good article that explains ISO cleanliness standards:

Understanding ISO Cleanliness Codes | Donaldson Engine & Vehicle

Learn what ISO cleanliness codes are derived from and how important it is to know the required oil and fuel cleanliness requirements for your equipment.

www.donaldson.com

This is the last fuel filter that came out of my Duramax, which filtered about 1,000 gallons of fuel. The filter starts out white.

2018 Duramax fuel filter in use for 14,000 miles

The filters always come out with this black coating. The new filter has white filter media. I wonder of the gasoline we put in our cars is as dirty as diesel fuel?

bobistheoilguy.com

 

[wpod]

It could be some bacteria.

 

[JHZR2]

Agree on bacteria being a concern if the car sat long periods with questionable care. I’d think the fuel system was well sealed and not conducive to bacteria, but you never know...

it’s pretty common to have junk in filters, even potentially due to some fuel lines that start to degrade. Could be any number of things.

 

[whizbyu]

I've always had the habit of waiting until the refuel light comes on to fill up. I will start refilling when 3/4 down from now on. Not sure if the lift pump is sucking the debris from the bottom of the tank.