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Thread: Fuel Tank Leak?

  1. #1
    Senior Member JoeRuscito's Avatar
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    Default Fuel Tank Leak?

    It seems I may have a tank leak. Now that my wings are complete I figured Id pressure test the tanks again with all of the fittings/sight tubes installed. I first tested them connected together at the main fuel supply ports and plugged the air vent line (with a plugged tycoon tube) and fuel caps (with sealing tape). I blew into the tanks enough to get the tape to bubble. I found this configuration leaked enough that the tape wasn't bubbled after about 12 hours. Then I separated the tanks to test individually. They both hold lung pressure for about 24 hrs before I can no longer see the tape is bubbled. So both tanks seems to leak at about the same rate and quite slow.

    Im wondering if I should be concerned or if this is what others have observed. Im wondering if the quick drain might leak air but not fuel. Or if the tanks should hold air indefinitely and I need to go searching for leaks at each of the fittings.

    Thanks for the help!

  2. #2
    Senior Member jrevens's Avatar
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    Default Re: Fuel Tank Leak?

    Hi Joe,

    It’s difficult to seal the filler openings with tape to make a perfectly air-tight seal. I found that aluminum duct tape worked best for me. So... you may or may not have leaks in the system. You can use a soapy water solution in a spray bottle to leak check, looking for tiny (or not so tiny) bubbles forming. If you have good seals on your filler caps you can connect balloons to the vent tubes as a pressure indicator also. Regarding the quick drain valves - if they leak air they leak fuel.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  3. #3
    Senior Member JoeRuscito's Avatar
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    Default Re: Fuel Tank Leak?

    Well it was the main pickup line. The fitting was leaking at the threads where the finger strained threaded into the tank. After talking to the factory my only option was to cut the elbow to unscrew and redo the sealant.

    For anyone out there that doesn’t have the banjo fittings. Get them. It would have been a simple fix if they were installed.

    Also, my suggestion would be to leak test the tanks for a second time just before covering and with all of the fittings installed. Just my two cents.


    Sent from my iPhone using Tapatalk

  4. #4
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    Default Re: Fuel Tank Leak?

    So you just removed fitting and it needed more sealant?
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
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  5. #5
    Senior Member JoeRuscito's Avatar
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    Default Re: Fuel Tank Leak?

    Yes. And also I may not have tightened enough. I was pretty conservative in tightening so as to not crack the tank. So when the elbow was level and what I thought was tight enough I stopped. Rather than going for a whole additional rotation of the strainer and risking cracking the tank. I hope that makes sense.

  6. #6
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    Default Re: Fuel Tank Leak?

    Yes thanks. Crossing my fingers for no leaks. I did test mine after installing fittings but not overnight.
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF......FLYING!
    N53TF......FLYING!

  7. #7
    Senior Member JoeRuscito's Avatar
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    Default Re: Fuel Tank Leak?

    I have two successfully tested tanks! Both held air while connected together for 24+ hours. I think Im good to go. Retrofitting for the banjo fittings was a bit of a project but got it done... highly highly suggest doing this from the start... Also the new sealant the factory is shipping, its blue, Needs to be added to both threads male and female to form a tight seal and before inserting needs to sit for quite a while (read 30 mins or so) for the solvents to evaporate. I originally only put the sealant on the male threads and avoided the last thread with the thinking this would keep from contaminating the tank/fuel... it seems for this stuff to work that thinking needs to be abandoned.

    Just my experience in case it helps anyone.

  8. #8
    Senior Member jiott's Avatar
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    Default Re: Fuel Tank Leak?

    Putting it on both threads sounds very bad to me; you will just push it off the female threads into the system-not good at all. Those instructions I believe are for when you use it to seal two flange surfaces. I would NEVER NEVER do that on a fuel fitting. One of the common causes of fuel system failure is pieces of teflon tape or other sealants in the fuel system causing blockages. This is very serious. Please call the factory and ask what they recommend for proper procedure with this new thread sealant they provide, then let us all know.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  9. #9
    Senior Member JoeRuscito's Avatar
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    Default Re: Fuel Tank Leak?

    That was also my original thinking! I will call to clarify once again...


    Quote Originally Posted by jiott View Post
    Putting it on both threads sounds very bad to me; you will just push it off the female threads into the system-not good at all. Those instructions I believe are for when you use it to seal two flange surfaces. I would NEVER NEVER do that on a fuel fitting...

  10. #10
    Senior Member JoeRuscito's Avatar
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    Default Re: Fuel Tank Leak?

    ...from the factory... "Yes we are using the new sealant and yes you should be fine.. You installed according to the directions.

    You will get sealant residual in the system and therefore a good practice is to clean the inline filters after about 10 hours of operation… Also be sure to sump the header tank.. especially the first fuel runs.. "

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