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Thread: Sealing leaking fiberglass fuel tank

  1. #1

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    Sealing leaking fiberglass fuel tank

    I have a Avid Flyer with fiberglass fuel tanks. One of the tanks has developed a small seeping leak. Are there any products such as sealers or sloshing compounds that anyone has successfully used to seal a leak like this? What advice do you have for repairing the tank? The factory formed fiberglass tanks that came with the kit were laid up with polyester resin which isn't resistant to alcohol and although I have been careful testing for alcohol in the fuel some contamination may have occurred.
    Any feed back on how to seal the leak will be appreciated.

  2. #2
    Anymouse's Avatar
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    Assuming this is just a pinhole leak and not a bigger problem, the repair on this is not that difficult. Mix up some of that polyester resin that the tank was made of. Put some negative pressure on the tank (it won't take much at all, and too much can cause more damage). You may be able to do this through your vent. Apply the resin at the source of the leak and let the negative pressure suck it in through the leak. Release the pressure, let cure and check to ensure the hole was completely filled.
    I'll come up with something profound

  3. #3

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    sealiong leaking polyester fuel tank

    I used the same vacuum procedure for sealing a leak in the end rib of my Glasair's wet wing fuel tank. Worked well but took a couple of rounds. I used a shop vac. Monitor the tank for signs of collapse while applying the vacuum...it doesnt take much. I measured the vacuum with a manaometer. Good luck!

  4. #4

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    Thanks for the suggestions. The tanks are molded to be a structural item of the wing and covered with fabric so access to the leak is limited. I'm hoping someone might have an easier solution other than removing fabric, recovering, and repainting. I will consider the clever negative pressure idea if I have to cut into the wing.

  5. #5

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    I was able to fix a pin hole leak on my COZY3 right strake tank using the slight vacuum method to suck in epoxy. Took me two trys. Finding the leak was the hard part. Put a slight presure on the tank and removed exterior and interior skin until I found the leak at the bottom of the level glass.

  6. #6

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    You can buy sloshing compounds from the usual suspects. they do take several days to dry, and are ideal if you cannot locate the source of the leak.
    If you know where the leak is, then it would be quicker to cut the fabric, do a fiberglass cloth and polyester ( or epoxy.) resin repair. Double check for more leaks then repair and repaint the fabric.
    Brian Evans.

  7. #7

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    Your problem is probably not due to fuel contamination. Years ago I had a similar problem with a fiberglass tank, and in the process learned that there can be a small pin hole somewhere in the interior which will allow fuel to wick along the fibers until it finds a pinhole or scratch somewhere on the exterior. I eventually ended up sloshing the enterior with commercial compound as well as painting the exterior with resin. I do like the vaccum and resin idea - especially with a thinner resin - something I should have tried! Good Luck!

  8. #8

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    Sealing Glass Tanks

    Bare glass laminates can be attacked by sustained exposure to mogas with ethanol, a slower deterioration with epoxy matrix but still degrading. Best solution is to coat exposed surfaces and block direct contact with a novalac resin which is more impervious to ethanol effects. These novalcs are an epoxy/phenolic compound under the name of Jeffco 9700 or Rhino 9700. They are commercially used as coatings for concrete floors and have low viscosity so they can be sloshed or brushed on. I have the Jeffco in my Pulsar glass tanks for 7 yrs with constant exposure to 10% ethanol Calif mogas and no leaks....yet.
    Bob H

  9. #9

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    Thanks Bob for the sugestions. Can Jeffco 9700 be used as a sloshing compound in a tank that has had fuel in it? I looked on the web for instructions and it appears that brushing it on is the most common usage. Any thoughts on how one would prepare the inside of tank that is installed in a wing and only accessible through the fill hole?
    Todd Madison

  10. #10

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    Sep 2011
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    Todd;
    Yes, the Jeffco will adhere to almost any surface, and as long as it is dry, should provide good adhesion. I have used it as an interior cowl coating for oil/fuel dripping and it withstands contact; does turn slightly yellow with time/exposure.
    If your tank is fixed in place, then sloshing would not work so only option is to brush coat. The smaller the opening, the harder to gain access to tank surfaces. I'd try a 1" wide brush attached to a bendable rod and try to touch all the inside surfaces with coating. Novalacs have really low viscosity and a little goes a long way for surface coverage. Mix small quantities, like 1/2 cup at a time, per mix ratio because it will exotherm in larger amounts, especially in warm weather.
    For anyone with glass tanks not installed, the time to coat is now when tank can be handled and sloshed.
    Bob H

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