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Old 27-10-2015, 21:39   #1
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Fixing fuel tank leak, found pit, sealing, how to clean?

I had discovered a diesel leak on my Gulf 32 that only happened when the tank was full. The tank on a Gulf 32 is 70 gallons, as is the water tank, which is part of why they are such great cruising boats for the NW where you often have to motor due to strong currents and fickle winds.

Anyway, the tank is also enveloped in a fiberglass blanket on all sides and bottom, and is suspended up off the bilge floor and keel by this fiberglass blanket.

I had determined that the leak was not from any leaking hoses or fuel fittings. It had to be from a leak in the tank itself. This tank came with no inspection ports, and the small hole for the tank sender is too small for getting a hand in. I had also fouled a few fuel filters too quickly and knew it was high time to clean out accumulated junk.

So today I launched into the project. My first step was to remove the remaining fuel. I had already run it down as far as I dared, to just about on E. I had never run this tank to E before and didn't know how the sender read. As we all know, every car tank reads E quite differently. Anyway, I brought my three 5 gallon diesel containers and started filling them from the fuel pump hose I pulled off the motor. I thought, maybe 10 gallons of the 70 gallons would remain.

I pumped out 10, and then 15. Damn. I had to run to the local hardware store and bought two more 5 gallon cans. I was astonished when those filled and I wasn't empty yet. I ended up pumping out an additional 3 gallons for a total of about 28 gallons when the darn thing started out just above E. Well now I have learned how my gauge reads!

The tank on a Gulf 32 is below the cabin sole and steps down from the galley to the dining area. Removing the tank would be worse than horrible. So I cut access holes today in the front and back. The tank is baffled and has three compartments. I can't access the middle compartment unless I cut through one of the baffles.

I found the tank bottom to be fairly coated in sludge and sticky goop. And a thin layer of water. 27 year old tank, so no surprises.

I'm happy to say I found a pit in the tank in the bottom of some of the sludge, which I had to scrape off with a razor blade. That pit allowed fuel to fill the envelope, and since it maintained the level of fuel in the tank, it only overflowed the envelope and leaked out when the tank was full.

So I am going to clean the tank thoroughly and use some flame master product to fill in the few pits and depressions. Only a few exist.

My question here is how you might go about cleaning those pitted areas. I'm thinking a good roughing up with 100 grit sandpaper would give it a good texture. The actual hole is only the size of a pencil lead.

So how would you clean this pitted area to prep it for a tank sealant?
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Old 28-10-2015, 00:28   #2
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Re: Fixing fuel tank leak, found pit, sealing, how to clean?

Use this stuff. Prep with a die grinder.



POR-15 Fuel Tank Repair Kit


Amazon.com: POR-15 Fuel Tank Repair Kit: Automotive


There is an associated filler. Just search a bit more on that product line.
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Old 28-10-2015, 10:01   #3
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Re: Fixing fuel tank leak, found pit, sealing, how to clean?

I appreciate the link but as I've said I've already researched and decided to go with the Flamemaster product for sealing. I'm sure there are many good things, but I've heard tremendous things about the aviation products.

Maybe they sell that degreaser separately? I am inclined to clean with acetone and a sander and maybe even a dremel in pitted places, to get down to good clean aluminum. Curious of any better methods?

I'm also wondering how people prefer to hold the inspection plate bolts upside down in the bolt hole long enough to get the plate and top nuts on. Maybe a dab of permatex on each one would do it.
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Old 28-10-2015, 10:06   #4
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Re: Fixing fuel tank leak, found pit, sealing, how to clean?

For the sealant used in wet fuel portions of aircraft structure, we used MEK as cleaner and clean up solvent. It's a step above acetone for that purpose with many things.
When I made a fuel tank, I tapped/threaded the inspection plate holes on the tank side, then I screwed bolts from inside the tank up so they protruded out of the tank like studs. Cleanance holes in the lid, nuts on top.
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Old 28-10-2015, 10:28   #5
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Re: Fixing fuel tank leak, found pit, sealing, how to clean?

Nice idea Cheechako. Threading the bolt holes would certainly do it, and not impact or prevent me from still using nuts on the bolts on top of the inspection plates to really snug them down. I'm familiar with MEK but hadn't thought of it.
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Old 28-10-2015, 10:37   #6
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Re: Fixing fuel tank leak, found pit, sealing, how to clean?

In fact, we were trying to phase out the use of MEK in our aircraft shop (due to all the worry about it) but the customer spec would only allow MEK to be used in that fuel sealant application.
Put some fuel resistant sealant under the bolt heads (inside the tank)
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Old 28-10-2015, 10:43   #7
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Re: Fixing fuel tank leak, found pit, sealing, how to clean?

Yes, it's all nasty stuff. I shudder to think about how my father treated all these solvents so casually but then he grew up on a farm in the South in the depression where just being alive was a gift after the age of 10. I just reread about MEK and it seems it is a slightly less aggressive solvent than acetone but benefits from slower evaporation. Same toxicity.
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Old 28-10-2015, 10:48   #8
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Re: Fixing fuel tank leak, found pit, sealing, how to clean?

I used to wash my hands and forearms in a bucket of acetone after doing fiberglass work. So I don't worry a heck of a lot about a bit here and there!
I heavily researched MEK in my time as a Health and Safety Manager. It's amazing what they do to rats trying to find out if it causes cancer etc. I mean they inject the stuff right into the rats for a long time and even then only a few of them get cancer...
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Old 28-10-2015, 11:06   #9
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Re: Fixing fuel tank leak, found pit, sealing, how to clean?

There will indeed be a special hell for humanity for how we have treated animals in the name of our research, and mind you, I was a Zoology major and not a vegan or PETA person. Nasty stuff in the name of research.

Anyway, my dad lived to 76 and it was the cigarettes that killed him, not the gallons of solvents and oils and caustic chemicals he bathed in every day. Lung cancer is no fun at all.
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Old 28-10-2015, 11:13   #10
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Re: Fixing fuel tank leak, found pit, sealing, how to clean?

Quote:
Originally Posted by bwindrope View Post
There will indeed be a special hell for humanity for how we have treated animals in the name of our research, and mind you, I was a Zoology major and not a vegan or PETA person. Nasty stuff in the name of research.

Anyway, my dad lived to 76 and it was the cigarettes that killed him, not the gallons of solvents and oils and caustic chemicals he bathed in every day. Lung cancer is no fun at all.
Gotta agree with you there... OK... done with this thread drift! sorry...
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