Micron size filters

It is likely algae or some microbial growth on top of a thin layer of water at the bottom of the tank. Shock treat tank with Sta-bil or Bio-bore or whatever local marina sells.

I'm going to suggest that you send some of that "SAMPLE" in the jar to a testing lab and find out positively what it is.

I will guess it is water, at least partly.

Just because you used a test strip does not guarantee it is not water.
Many tanks have a sloped bottom or the vessel may not be dead level so neither is the fuel.
Water will settle in the lowest tank corner and unless you KNOW that test strip got into that corner you don't know that you don't have water.

As mentioned you really do need to examine the tank for any rusted holes on top and around the filler neck where it joins the tank. If the tank top is wet there is water so find the source and stop it.

Make sure there are O rings sealing the filler cap to the deck filler fitting body and that any present are in good condition or they may not seal. Grease them also with a water resistant grease such an as outboard motor prop shaft grease .

Ensure the deck fitting itself is sealed to the deck.
Check that the hose is securely clamped to the deck fitting nipple.

A wee story I have shared before: A dock neighbour was going nuts over water in his tank. He would clean it out, getting rid of the watered fuel. Next time after a rain storm he would have more water.
Checked all kinds of things. Vent line, deck fitting cap seals. It took several tries and a lot of work but it turned out to be an improperly sealed to the deck, deck filler fitting allowing water to get under the deck fitting, then run down the nipple the tank hose attached to where the hose was poorly or not clamped and run into the tank.
Once he took care of that the problem stopped.

Of course the dirt/water could be from a dirty supplier.

BUt I suggest you need to find out what that really is as it may suggest a source.

You need to find the water source and stop it. THen get the water out and ensure it stays out. Only then try a biocide. Doing it now will not eliminate the cause of any biological problem, the water. Also if there is biological action the bodies will likely overwhelm the filters. The water as mentioned could overwhelm your filters in less than ideal conditions.

If you're using biodiesel, there's glycerine in it. Biodiesel in higher concentrations will act as a solvent, cleaning any tank sludge too quickly.

I've been dealing with diesel since the late 1950s. I always add a quality fuel conditioner when I fuel. I never have fuel problems and run a 2 micron filter in my Racors. The diesel we have today is much worse than the diesel of 1960. Stored w/o conditioners, it tends to separate into base elements that like to absorb water.

Most good fuel conditioners have an additive that helps the fuel filter (like a Racor) separate out water. Better conditioners also have a catalyst that improves fuel burn.
I think you have a water problem and need to use a good conditioner, not just what the local marina happens to sell. The ones with a catalyst will improve your fuel mileage. Mine gives me a 6-10% better mileage (depending on how much I add) and pays for itself.

All great advice! I never used biodiesel, so that's off the table, but I am going to check the tanks for leaks. The fuel fills don't run straight into the tanks, poor planning when you think that you could put the deckfill directly above the tank, so I can't get a sample without opening the inspection ports, which I believe will be my first order of business. I'll try some Biobor and see what that will do. I'll keep you all posted on progress, in the meantime, thanks for all the great advice and ideas.
Jim

Whether the orings on the fuel caps look good or not, replace them annually, probably costs less than a dollar a piece. Orings get compressed over time, and can get pinched while the cap is installed. Also check where the oring seals on the deck fill and cap for corrosion and pitting. Finally, check the cap where the tool engages to unscrew it. Found a small hole in one from a casting flaw.

Ted

VL
Two questions
- how old is the oldest fuel in your tanks?
- are you 100% confident of your supplier?

As mentioned, you can’t go wrong by following sbar marine. It is a great website to learn about marine filtration. Like anchors and chart plotters you will find lots of opinions, sbar will provide you facts.

I use a 900 series Racor with 10 micron first then a Racor 500 with 2 micron after, the 900 has the capacity to go for quite awhile before changing and catches most of the water then the 500 gets the small stuff and any remaining water before the fuel goes to the engine filter. I also have the 900 plumbed to serve as a polishing filter for which I replace the 10 micron with a 2.

VJameslanza said:

George, the coolant is yellow, but why would that have anything to do with the fuel from the tanks? The green stuff is kind of lumpy, but liquid-like. You can see it a little better in this photo. The color like Archie mentioned does look like anti-freeze that's been in an engine way too long.

The color of this is through a thin layer of dyed diesel, the color is still quite bilious green, this photo was just to give you some idea of what the 'junk' looks like.

I really do appreciate all the input gang, that's what I love about the TF, lots of knowledge, lots of opinions, lots of ideas as to which way to go.

As I mentioned in my earlier post, I cut open the filters, and there was absolutely nothing in them, no grit, no small pieces of dirt and definitely none of that green stuff. So the coalescer is doing its job spinning the junk out of the diesel.

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To see if it is water you can put a small amount in the freezer and see what happens. You can also 'drip' a small drop on a heated plate outdoors and see if it splatters.
When you get the inspection plates open you can run some flexible copper icemaker line to the bottom of the lowest point in the tank and use a vanepuppy type pump to remove whatever this stuff turns out to be, Pulling from the bottom untill you get to clean diesel when the tanks are very still will work to eliminate most of the contaminants.

sunchaser said:

VL
Two questions
- how old is the oldest fuel in your tanks?
- are you 100% confident of your supplier?

As mentioned, you can’t go wrong by following sbar marine. It is a great website to learn about marine filtration. Like anchors and chart plotters you will find lots of opinions, sbar will provide you facts.

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This is the best advice IMO.

VJameslanza said:

Where would anti-freeze and diesel fuel find a common location in the engine? The oil, recently changed shows no indication of water or foreign matter. But the closed cooling system and the fuel delivery system (pump, injectors, return) don't seem to 'overlap' at any point.

Please keep the opinions and ideas coming, we might be getting close.
Jim

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Point well taken, unless there is a fuel cooler on the return side, which is typically where they are.

Getting a sample tested is the best idea I've seen here.

There's no fuel cooler, and there's not enough water in the 'mixture' according to Gasoila WFP to turn the test strip from brown. The best advice I think I've had is to try to draw a sample from the lowest place in the fuel tanks. I liked the 'copper tube' idea. I thought that if I connected it to the pump with a clear vinyl hose I could pump the what ever the heck it is out till I get some clean diesel. The problem is there are no inspection ports, so I'll have to go through the fuel sender at the top center of the tank...I wonder why they never put a tap at the lowest point in the tank? Seems like it would be a relatively inexpensive way to 'clean' or 'polish' your fuel. Just my 2 cents.

Comodave said:

I run 10 micron primaries since the secondaries are a pain to change and bleed.

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Yep. though I run 2 Micron

psneeld said:

While step filtration is fine and really the preferred method, many of us running 2 gal per hr diesels have run 2 micron primary and secondary filters for decades with great results.

With a vacuum gauge, you can tell if there is a strain on the fuel pump.... and go from there.

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exactly

VJameslanza said:

There's no fuel cooler, and there's not enough water in the 'mixture' according to Gasoila WFP to turn the test strip from brown. The best advice I think I've had is to try to draw a sample from the lowest place in the fuel tanks. I liked the 'copper tube' idea. I thought that if I connected it to the pump with a clear vinyl hose I could pump the what ever the heck it is out till I get some clean diesel. The problem is there are no inspection ports, so I'll have to go through the fuel sender at the top center of the tank...I wonder why they never put a tap at the lowest point in the tank? Seems like it would be a relatively inexpensive way to 'clean' or 'polish' your fuel. Just my 2 cents.

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Did you taste it?
That will tell you right away what it is.
Looks to me it's water with organic growth.
Taste taste will tell.

I'd clean your tanks as best you can, but don't be too worried. Your system has taken care of it.

Replacing deck fill O rings, put grease on them top and bottom. A little should squeeze out when you nip up the cap. I think it helps, was advised to do it by an ex Navy mechanic who served on subs.
PS. I hate flush mount deck fuel fills, a 100% recipe for trouble.

Richard,
TASTE IT? Did you see the picture of it? I hate eating my vegetables, the thought of putting even a drop of that on my tongue gives me chills and shakes (not the good chocolate shake kind). And if I was able to repress my gag reflex, exactly what would I be tasting? Is it like a pickle? Stringbean? I don't know...

BruceK said:

Replacing deck fill O rings, put grease on them top and bottom. A little should squeeze out when you nip up the cap. I think it helps, was advised to do it by an ex Navy mechanic who served on subs.
PS. I hate flush mount deck fuel fills, a 100% recipe for trouble.

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I'm with you, I never understood how flush fills made sense, especially on boats. The boat I'm putting together now has the fills in a small watertight compartment with a hatch over, not only keeps them dry but acts as a cofferdam when filling.

".I wonder why they never put a tap at the lowest point in the tank?"

The boats first purchaser did not ask for it .

A real bailable sump would be ideal, but might mess up the interior layout and cost a bit.
Our USN monel tanks have both a low point drain and a fitted plate just above the tank bottom to keep mungus from swishing up and mixing with the feel in rough going.
Almost as good as a proper sump. The tank fitting has a valve and a plug , just to be safer.

Next time you fuel you might want to use a BAJA filter to see if its coming from your fuel source.

Fish53 said:

I use a 900 series Racor with 10 micron first then a Racor 500 with 2 micron after, the 900 has the capacity to go for quite awhile before changing and catches most of the water then the 500 gets the small stuff and any remaining water before the fuel goes to the engine filter. I also have the 900 plumbed to serve as a polishing filter for which I replace the 10 micron with a 2.

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Hi,

And if you use the original Parker / Racor filters, the Aqua block filter material that predates the water molecules, which keeps the fuel system in better condition to prevent water from ~100%.

NBs