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Old 19-11-2021, 08:08   #31
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Re: Gunk in the fuel tank

Once you get the problem resolved, you may want to consider replacing the o-rings on your deck fills. Degraded o-rings are likely how the water entered your tank in the first place.
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Old 19-11-2021, 09:36   #32
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Re: Gunk in the fuel tank

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Originally Posted by boatpoker View Post
What she said .....
Hi,

I bought a boat a few years back that had been sitting for over 10 years, with fuel in the tank. Lots of gunk and whatever in there. I pumped out what I could from the tank using a hand siphon pump. (you need to get rid of all that old fuel, and since it was diesel, brought it to jiffy lube for recycling). Then I attached clean rags on the end of a stick and did my best to wipe as much out of the tank as I could. Then I used lots of sea foam, pouring it in the tank,swishing it around with a stick, pumping it out. Putting new sea foam in, repeat until it comes out clean. Once I did that, I put in fresh diesel, and the engine was good to go (with new fuel filter). I was quoted a very high price from a company to clean the tank, but my method did the job.
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Old 19-11-2021, 09:48   #33
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Re: Gunk in the fuel tank

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Originally Posted by bhillmail View Post
Hi,

I bought a boat a few years back that had been sitting for over 10 years, with fuel in the tank. Lots of gunk and whatever in there. I pumped out what I could from the tank using a hand siphon pump. (you need to get rid of all that old fuel, and since it was diesel, brought it to jiffy lube for recycling). Then I attached clean rags on the end of a stick and did my best to wipe as much out of the tank as I could. Then I used lots of sea foam, pouring it in the tank,swishing it around with a stick, pumping it out. Putting new sea foam in, repeat until it comes out clean. Once I did that, I put in fresh diesel, and the engine was good to go (with new fuel filter). I was quoted a very high price from a company to clean the tank, but my method did the job.
I had my aluminum fuel tanks built with the feed coming from the bottom. Nothing sits in the bottom of my tanks but diesel. any miniscule contamination or water gets trapped in the filters.
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Old 19-11-2021, 10:34   #34
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Re: Gunk in the fuel tank

I pulled the tank out completely (all the way from under the transom, behind the aft cabin - was a pain, but worth doing it right and doing it only once). Completley fixed it and now I never worry about it.

So for you I would suggest the same:
1) pull the tank out if you can and power wash it
1a) if you can't pull it out - open it and clean while in the boat
2) get rid of the old fuel (if it is not a huge amount). Yes, you can polish it, but it's a pain and you may not get everything out.
3) top off your tank whenever possible, so there is no empty space and a chance for condensate to form
4) Use biocide
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Old 19-11-2021, 14:40   #35
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Re: Gunk in the fuel tank

I had a similar problems some years ago. I had my tanks drained and an access port cut in both tanks. There was 5 gallons of red jelly goo in each tank.. Tanks were cleaned and lines purged and all good. I recently had my boat in the yard for 3 weeks and had the same process repeated last week. No goo but a lot of water after the boat was not used for 5 months. Cleaned tanks, purged lines. Clean your tanks, hange filters and keep your tanks full to avoid condensation.
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Old 19-11-2021, 20:45   #36
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Re: Gunk in the fuel tank

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Originally Posted by MicHughV View Post
Some years ago, I put a new engine in my boat.
To do this required moving a diesel fuel tank first.

Being curious, I opened the inspection plate located on top of the tank to view inside.

I was amazed to see the bottom and lower sides covered in what looked like a black slimey goo...I'm going to guess....1/8 -3/16" thick...
I was fortunate that the pickup point for the fuel delivery system was about 2" above this level.

I've read several reasons for the cause of this, but removing it...none, besides hard labor. It would have to be scraped off and cleaned somehow....pressure washed most likely. The prospect of doing this seemed daunting to me. Without an inspection plate access, this would be next to impossible.

Considering my options, I had a new tank built.
Had a similar black buildup in our tank as well as water etc. P.O. had no o-ring on deck fuel cap causing so much gunk that filter clogged. We were away on a 6 wk trip so I removed the 18 litre tank & put petrol (gasoline) in it & sloshed it around & I think it dissolved the black stuff but it was 8 years ago so i'm not positive as memory is variable. I do remember that it was very black the rinse petrol that came out & I had to do a couple of rinses before it was cleanish. Didnt have any more problems after that with an o-ring on the deck fill cap & still using the same fuel filter that I replaced at that time but we only have an 8hp diesel engine that uses 600cc per hr
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Old 20-11-2021, 06:10   #37
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Re: Gunk in the fuel tank

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Originally Posted by Mickeyrouse View Post
So here’s what I did: it didn’t appear that any products were available that would break down the emulsified fuel. So I ditched it. I used an extra-long pickup tube (touched the tank bottom) to get as much out as possible. Surprisingly, what did come out didn’t look too terrible.

I ran clean fuel thru the system before I started it to purge any miscreants. I used the recommended amount of Howe’s diesel treatment (“America’s #1 selling diesel additive”… must be good, right?) a product that claims to break down gelled diesel, kills bacteria, dissolves water…..shines your shoes, etc. etc.

Also changed a line to the Racor to be sure there’s no air getting in. Ran the engine with a slight load for 45 minutes, all is good.
Thanks for getting back to us, Mickey. It's always great to hear when a problem has been resolved.

As far as how the fuel looked - yeah, it's surprising, isn't it? See the pictures (below) of foul diesel. With all the comments about black goo and sediment and/or jelly, any of us might expect the fuel to look like black tar. But nope. These pictures are all examples of fuel that will cause problems.

I also like the other posters' suggestions of adding/replacing the fuel fill o-ring to eliminate an additional source of water ingress. MicHugh's story of the wasp mud dauber's nest blocking the tank vent was also priceless!

Fair winds!
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Old 12-12-2021, 18:06   #38
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Re: Gunk in the fuel tank

I agree with all of the tank washing recommendations and then to keep it from coming back try a product called Fuel Right which dissolves the slime forming bacteria which then exits the fuel system and is burned with the fuel.

It also coats the fuel filter, hoses and tank that is in contact with the treated fuel. Biocides just kills most of the bugs with each application but, unfortunately, do nothing to totally rid of the bacterial. In addition, the Yanmar operations manual recommends against them.
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Old 22-12-2021, 13:23   #39
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Re: Gunk in the fuel tank

I holesawed (4") access holes - 6 in each tank then made and put in 6" HDPE covers.
Usual jelly inside.
I extended the pickup to the base of the tank with a brass T
That way it can suck up water and gives 2 paths for pickup. Water will get into filters rather than sit in tank.
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