Slimy stuff clogging my fuel filter

[brico]

Ever since I purchased my 1980 Hattaeras 37 with twin Detroit Diesels in 2014 I had a little hazy fuel in the bottom of my Racor filter bowl and my fuel filter on Port engine would clog up sooner than the Starboard one. I replaced the rubber "O" ring on the deck filling plug and in 2019 I got the Port tank opened (just a small port on the top) and flushed by fuel polishing service and I did not take any fuel back but left it empty to dry out and refilled with fresh fuel. At that time (before opening, flushing and polishing) I measured 1/2" water in the bottom of the Port tank using KolorKut paste.

Since then my Port fuel filter has started clogging faster and more frequently than the Starboard one again. It was so bad that I could not run the Port engine on WOT as there was no sufficient fuel supplied. When I opened and cleaned the filter bowl I found some greyish/brownish slimy stuff and filter element completely clogged up. Before that we were going fishing and trawling in some chop so boat rocked and rolled pretty heavily so I guess all that slimy stuff was picked up by the fuel pump. Today I checked again with KolorKut and found only traces (1/16") of water on the sounding rod dipped to the bottom of the tank. I dipped the Starboard tank and found almost 1/2" of water/sludge using the KolorKut paste. I could even feel the bottom being covered with some sediment as I dipped it.

I've not opened the Starboard fuel tank yet. I replace the filter every 100 hours of running and gauge on it is not going to vacuum.

On the Port tank I replace the filter almost every 30 hours of running, (more frequently if in choppy weather) and always have sediments and slime on the bowl.

Would application of "Biobor JF" fuel additive help with the problem I have? It would appear that with less water in the tank I still get more debris clogging up my filters. so possibly some growth is happening in the Port tank.

Both tanks are fiberglass. I have to admit I do not top up the tanks at the end of the season so possibly some condesation during wet winter months here in PNW. But cannot understand why with less water traces I get more sludge/slime than the Starboard tank.

Any suggestions are welcome.

[Avenger]

Bacteria live in the interface between fuel and water. You will need to use Biobor or a similar biocide, but be prepared to get the fuel polished or change a LOT of filters.

You'll still need to find the source of the water or the problem will re-occur.

Also, are you using a fuel additive? That "cloudy" fuel may indicate a water dispersant. Water dispersant is a no-no for diesels.

[rsmith]

Once the alge starts growing it won’t stop until you kill it with biocide but you will be left with the dead algae to get rid of. It dose settle to the bottom where with a copper tube you can suck a lot of it out with a small pump or shop vac.
If you don’t fill the tanks after every run condensation is just a fact of life. Even with fuel coolers Detroits return hot fuel to the tanks.After any good run you feel how warm the tanks are. As you use fuel moisture laden air is drawn through the vents to replace the fuel used. The vents in the side of the hull are the worst place for picking u spray and water droplets. This air is constantly being sucked into the vents. At the end of the day you have warm tank with fuel and supersaturated air as it cools down the water comes back out as condensation. The only way to stop it is to fill the tanks after each run to force the air back out before it cools. It’s just a fact of life in the marine environment.