Brown stuff in fuel tank?

[MoBear]

Hi all,



New boat owner, emptied my diesel tank (to replace the fuel line that was kinked and with no shut off valve), and am trying to clean them. Most of the tank is pretty clean, but the bottom corner is all brown. I tried scrubbing it with a plastic scrub brush and it didn't even make a dent in it. The tank is stainless steel and the boat sat on the hard for 10 years before we bought it. (We didn't know that at the time, found out after purchase - the previous owner finally put it back in the water and started working on it before we bought it).


I have been trying to find info on what it is and how to clean it, but I'm still not sure. It is completely hard and dried, so it doesn't 'look' like the black sludge or the bio issues people talk about - but maybe that is just because I let it dry?


Taking the tank out would be nearly impossible, so I really want to do this in place. Any suggestions on what it is, and what is safe to use for cleaning it (or if it is ok to leave it as is?) is much appreciated!
(picture is attached)



Thanks all!

[Jammer]

It's what is colloquially called "varnish," which is fuel that has deteriorated and polymerized.

I believe that the safest way to remove it is with one of the "gallon bucket" type carburetor cleaners such as the ones sold by NAPA under the "Mac's" brand or by Gunk. The primary solvent in these is 2-Butoxyethanol, which is less toxic and less flammable than the various alternatives. It will take an overnight scrub and soak. Keep in mind that "less toxic" and "less flammable" does not mean harmless, it will still burn and you should still wear gloves. Think in terms of an overnight soak and some brushing.

You can use a spray carburetor cleaner but these are generally more flammable and toxic as they contain mixtures of acetone, methanol, toluene, MEK, etc.

[MoBear]

Originally Posted by Jammer

It's what is colloquially called "varnish," which is fuel that has deteriorated and polymerized.

I believe that the safest way to remove it is with one of the "gallon bucket" type carburetor cleaners such as the ones sold by NAPA under the "Mac's" brand or by Gunk. The primary solvent in these is 2-Butoxyethanol, which is less toxic and less flammable than the various alternatives. It will take an overnight scrub and soak. Keep in mind that "less toxic" and "less flammable" does not mean harmless, it will still burn and you should still wear gloves. Think in terms of an overnight soak and some brushing.

You can use a spray carburetor cleaner but these are generally more flammable and toxic as they contain mixtures of acetone, methanol, toluene, MEK, etc.

Thank you for the quick and very helpful response!

Second question - is it safe to leave it? Will it cause me issues if I do not clean it out? (Not super excited about using dangerous chemicals - but will if I have to...)


Also - if I do need to clean it - do I need to do anything after I clean it before adding fuel again? Does the 'cleaner' need to be cleaned out? (obviously removing the fluid, but does it need to be wiped down or anything?)


Thank you again!

[ulul]

Without sounding like a “nanny” too much, remember to keep in mind when working in the enclosed space of a fuel tank (and engine compartment) with extremely volatile cleaning/solvent fluids, that a minor spark from fan motors, old drop lamps, static, etc…can have explosive and serious burn consequences. I might start with the least (or non) volatile and elbow grease if useable in the enclosed space.

[MoBear]

Originally Posted by ulul

Without sounding like a “nanny” too much, remember to keep in mind when working in the enclosed space of a fuel tank (and engine compartment) with extremely volatile cleaning/solvent fluids, that a minor spark from fan motors, old drop lamps, static, etc…can have explosive and serious burn consequences. I might start with the least (or non) volatile and elbow grease if useable in the enclosed space.

Thank you - that is my biggest worry too. It is a small space without a lot of venting so I'm a little concerned about any dangerous chemicals. I tried basic elbow grease, but I'm not sure what other non-volatile things I could use without causing other issues.


I'm leaning towards wiping it down as best I can, using a shop vac to get any last particulate out, and then leaving it as is and keeping a couple spare fuel filters on board just in case....


It does have two fuel filters installed in addition to the fuel/water separator, so a little redundancy there

[Cheechako]

Originally Posted by MoBear

Hi all,



New boat owner, emptied my diesel tank (to replace the fuel line that was kinked and with no shut off valve), and am trying to clean them. Most of the tank is pretty clean, but the bottom corner is all brown. I tried scrubbing it with a plastic scrub brush and it didn't even make a dent in it. The tank is stainless steel and the boat sat on the hard for 10 years before we bought it. (We didn't know that at the time, found out after purchase - the previous owner finally put it back in the water and started working on it before we bought it).


I have been trying to find info on what it is and how to clean it, but I'm still not sure. It is completely hard and dried, so it doesn't 'look' like the black sludge or the bio issues people talk about - but maybe that is just because I let it dry?


Taking the tank out would be nearly impossible, so I really want to do this in place. Any suggestions on what it is, and what is safe to use for cleaning it (or if it is ok to leave it as is?) is much appreciated!
(picture is attached)



Thanks all!

Is that a glass tank? If so it is likely just stained, permanently. Either way it sounds like it's clean. You rely on filters to get any final thing out before the engine. It's nice to start with a good clean tank though, good for you!

[Jammer]

It's harmless as long as it stays attached to the tank wall.


The potential problem is that if it later dissolves, breaks apart, or comes unstuck it can potentially clog stuff -- fuel outlets, fuel lines, fuel filters. It's a judgment call whether to leave it and it's hard for me to tell from your photo how much there is and how tenaciously it's attached to the tank.


I'll tell a little story.


Once upon a time, maybe 20 years ago or so, Biodiesel was a cool new thing. The US Department of Defense decided to do some testing with it to determine its suitability for use to make the armed forces more sustainable and environmentally friendly (no, I'm not making this up). One of the first experiments they tried was to use it in place of #2 fuel oil for the furnaces in family housing in one or another of their bases. So that fall they filled up the fuel tanks -- a mixture of underground and basement tanks as I recall -- in a couple hundred houses with biodiesel.


The furnaces all failed on the second or third cold day because the fuel strainers were clogged. They cleaned and replaced a bunch of strainers and filters and probably more than a couple of pumps and nozzles. If you've ever lived in a house with a fuel oil furnace, you know how fiddly they are.


It happened again a couple of days later. Every one of them, clogged up. After another round or two of this they installed large secondary filters, like the Racors we use. Those too clogged at least in some cases and required ongoing periodic replacement extending through the first winter.


The biodiesel was, of course, pure and clean and free of anything that could clog the filters. But one of the characteristics of biodiesel is that, being an ester, it has much greater solvent power than ordinary fossil-derived diesel, which is an alkane. The biodiesel was dissolving decades of accumulated crap -- mostly varnish like what you see -- from the sides and bottoms of the tanks. Then it broke up into pieces, formed some sort of cloudy suspension, and clogged the filters.


And that's what you've got to watch. Take on some biodiesel or maybe have some well-meaning mechanic pour in some kind of fuel system cleaner additive that actually works, and whatever's in your tank will come apart and start clogging things.

[Searles]

Diesel varnish will eventually dissolve in fresh diesel over time ,BUT it will then block up your fuel system ,if a metal tank acetone will dissolve the varnish , BUT be carefull .⚓️⛵️