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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 02-07-2009
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Smile New Fuel Tank - questions

My 20+yr aluminum diesel tank developed a slow leak this past season. I get a small amount of fuel in the bilge after a week or so on the mooring, especially after I top off the tank. I thought I should repair this asap.

I though I might access the tank through the sending unit opening, drain the fuel, clean the insides, and find the hole or crack to seal from within. The problem is, the opening at the top is so small, I can't really see much inside. To make things more difficult, the fuel tank is completely glassed-in under the port lazarette, so there's no other access.

So here's the question: do I cut out old tank out and replace it (a big messy job), or can I just leave it there (empty, of course) and buy a Moeller-type tank to install above the old one. I have room above the old tank, inside the lazarette next to the holding tank. Is there any problem leaving the old tank where it is? I'd rather not cut any fiberglass if I dont have to.

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Old 02-07-2009
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sailor :
One option is to cut a big section out of the top of the tank for access, then cut a hole in the floor of the tank for drainage, then clean it like crazy using the hole for drainage of the detergent solution.
When it is super-clean, weld a wee patch over the hole in the tank floor... watch your fire risk with the radiated heat!!!!... then seal the tank with two part polysulphide.
To leak test the tank, you will have to flood the ship right up to the floorboards in order to see if it is leaking.
Finally, flood the tank to the brim with water (to mitigate the fire risk) and weld a new top onto the tank Iinclude an inspection hatch), and weld the top on again.

In 1997 I had to go through this whole ritual. I never fill the tank to the top ever.... it is simply too hard on it.

To my horror, the tank still leaked if I filled it more than about 35 gallons, so I don't.
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Old 02-07-2009
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There are a number pf liquid epoxy type(The exact chemical comp may differ from epoxy or polyurethane) fuel tank repair substances. I haven't used any off the web, but used a composition from Eastmans auto restorers catalog many years ago with great sucess on my tractor fuel tank. You remove the tank, pour this stuff in and shake the tank to coat the inside. I would start there. wes carroll
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Old 02-08-2009
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Well, I tried to cut back some of the fiberglass over the tank, and found that it is merely a thin layer placed over thick plywood covering the tank. I am concerned about the structural integrity of the boat if I cut this wood away.
Maybe I could cut a new piece of plywood to fit, and then glass it all in afterward...

...Or should I just leave the old one in there, get a new plastic tank and secure it in the lazarette?
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Old 02-09-2009
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What about a picture or two?
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Old 02-09-2009
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I am not sure what your lazerette or tank area look like but if you are concerned about the integrity of the boat then support everything that is being supported by the plywood then cut out the old section, repair or install new tank and put back the plywood etc. One thought if you are not removing the entire piece of plywood then you may not need to worry about the integrity since you will still have some support. If you are not going to move the boat etc. during tank extraction what could be the harm? Consider all that is being supported then support as necessary or consider leaving as much plywood as possible. If its the floor to the cockpit it my not matter that much just cut out what you need to remove the tank. I would seriously consider removing the old tank and repair. In the future you might be glad you did since you could have a headache trying to secure an old tank on new. Besides do it right the first time even if it takes more time vs. a quick fix. As posted above, pictures would be helpful to see your problem.
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Old 02-09-2009
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Cutting the top of the tank off would allow you to insert a fuel bladder into the old tank after removing the baffles. But cutting the floor out is something that cannot be addressed with current info.

What type boat is it? Have you looked on an owners site? My boat is known to have the tank issue and the Endev owners site is full of suggestions on what to do. Mine is brand new, thanks to the PO!
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Old 02-16-2009
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I finally got down to work after avoiding the inevitable. I decided to tear out the old leaking diesel tank, and I am really glad I did. After struggling to move the oddly-shaped aluminum tank out of its well between the stringers, I found about two gallons of fuel in a puddle OUTSIDE the tank! No wonder we had such an awful smell all the time!

Now, after trying unsuccessfully to maneuver the tank through the lazarette opening, I realize it must be cut apart.

So here's the next question: will the diesel fumes ignite in the tank if I try to sawzall it apart? I will try to drain it empty of diesel as much as I can, but is it dangerous to make sparks? I know it's not gasoline, but better safe than sorry. My internet searches on the topic are inconclusive.

TY
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Old 02-16-2009
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To be honest, I am not really sure if fumes would be an issue. I think it should be ok since the tank will be able to vent out the hose connections. That is if the hoses are disconnected. Beyond that, diesel has a relatively high flash point and it would take some hot sparks to iginite it in air (e.g., >100 F ?). If I remember correctly, diesels run on compression not on an ignition source. That is no spark plug, so I am thinking the sawzall should be ok. Have you tried calling a diesel garage or scrape yard?

I just pulled my tank this weekend with the intention of installing (cutting) an inspection port in about two weeks. Hopefully, I can let you know how cutting the port goes. Seriously though I am not to concerned since I was able to drain the tank down to nothing using a jabsco hand pump and no fuel was in the tank while pulling out of the hold.

My question to you is how are you going to install a new tank if you cannot remove the whole old tank?

Last edited by ambianceack; 02-16-2009 at 07:02 PM.
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Old 02-16-2009
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Can you soak up the fuel with old rags and put them into a plastic bag for disposal?
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