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Thread: Non-vented fuel tank - leaking?

  1. #1
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    Feb 2016
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    Madison, Connecticut, USA
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    Default Non-vented fuel tank - leaking?

    Hey all,

    I went to take the boat out tonight, a flat bottom skiff, and noticed about a gallon of gas sloshing around the stern and a mostly empty fuel tank. I have no idea how this happened, but I'm assuming the build of pressure inside the tank pushed the gas up through the fuel line and somehow leaked out from there. I went ahead and ordered a new tank, still EPA approved unvented, just in case there was a hairline crack in our existing tank but I'm not sure how to proceed. I do not want the pine bottom planking soaking in gasoline whenever the sun is out, and I certainly don't want any ignition as the boat is parked between two boats much more expensive than mine.

    Should I leave the gas cap a 1/2 turn open so air can escape? What's a solution?

  2. #2
    Join Date
    Oct 2009
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    Default Re: Non-vented fuel tank - leaking?

    Is this a portable 6 gallon tank or a built in jobbie?
    I might try some clay to soak up gas residue on the pine planks after you sponge the bulk . Is it 2 cycle gas ...all oily?

  3. #3
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    Feb 2016
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    Madison, Connecticut, USA
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    Default Re: Non-vented fuel tank - leaking?

    It's a portable 3 gallon tank. No oil - 4 stroke outboard

    Good idea on soaking up the residue

  4. #4
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    Mar 2017
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    Indian Land, SC, USA
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    Default Re: Non-vented fuel tank - leaking?

    Do you have a primer bulb in the fuel line ? Thinking maybe failed from UV degradation.




    Rick

  5. #5
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    Default Re: Non-vented fuel tank - leaking?

    When you say "non vented"...does the cap not have an air vent screw?

  6. #6
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    Mar 2007
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    East Quogue,NY
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    Default Non-vented fuel tank - leaking?

    Test the tank with water to see if its leaking.

    I doubt pressure had anything to do with it, per se. However, if your primer bulb, or either of the fuel line fittings or the demand valve failed, you might get a siphon going or fuel flowing. Does the bulb get hard when you squeeze it ? ( staying soft indicates a bad check valve)

    Disconnect the engine end and remove tgst fitting... is fuel coming out?

    Bruce... new tanks, like new gas cans, have to meet stricter federal vapor ( " evaporative emissions") regs and aren't vented like old school tanks anymore.

    Kevin




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  7. #7
    Join Date
    Oct 2018
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    tyler, texas, usa
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    Default Re: Non-vented fuel tank - leaking?

    You can buy replacement vented caps for your old tanks. The fit the new tanks, but you're not supposed to use them.

  8. #8
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    Apr 1999
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    Hyannis, MA, USA
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    Default Re: Non-vented fuel tank - leaking?

    These tanks have a one-way vent often fitted on the fuel hose between the tank and the bulb. It admits air into the tank as needed but prevents gas vapor getting out. Given its location in the fuel supply, if it fails and the tank develops positive pressure, it will force liquid gas out. Perhaps it's either failed or was installed backwards or is not there at all.

  9. #9
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    Default Re: Non-vented fuel tank - leaking?

    I guess I'm using 20 yo tanks.
    Twenty years.... I still think of them as new....weird.
    This non vented sounds like a modern in convenience.

  10. #10
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    Nov 2011
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    Salt Spring Island, BC
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    Default Re: Non-vented fuel tank - leaking?

    I've noticed that gasoline expands a lot when it warms up. It wouldn't surprise me to learn that non vented tanks and fuel lines will fail under pressure often enough that there is a net increase in evaporative pollution.

  11. #11
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    Oct 2018
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    tyler, texas, usa
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    Default Re: Non-vented fuel tank - leaking?

    I've heard of folks drilling a very small (less than 1/16") hole in the fuel caps to allow the tank to breathe. During the Summer, we've had the non-vented tanks force fuel into the carburetor and fill the block with gasoline. It's also good to install a fuel shutoff valve close to the engine.

  12. #12
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    Oct 2005
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    seattle
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    Default Re: Non-vented fuel tank - leaking?

    I carry a new plastic 2.5 gallon gas can on deck. When the sun hits it it blows up like a balloon. Scares me so I open the cap and let it go back to its original shape. Then the sun goes away and the tank sucks in. A few cycles of this on my last gas can resulted in cracks in the side and I had to replace it. These new non-vented things are a disaster waiting to happen IMHO. I think I might get out my drill.

  13. #13
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    Oct 2018
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    tyler, texas, usa
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    Default Re: Non-vented fuel tank - leaking?

    They also sell the yellow vent caps, for portable gas cans, at various online locations.

  14. #14
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    Jan 2004
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    Newport News, VA
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    Default Re: Non-vented fuel tank - leaking?

    you can get an Attwood fuel demand valve. It absolutely will not pass fuel unless a suction occurs on the fuel line.
    I redesigned my fuel fill and tank to using a Perko VPR valved fuel cap that has the vent going back to the fuel fill.
    So the vent hole in the hull side is gone.
    With a VPR cap it is like your car, it is double spring valve vented, hold 1 psi either pressure or vacuum in the fuel tank.
    The fuel demand valve prevent a 1 psi pressurized tank from leaking fuel into the boat if you disconnected a fuel line.

    My Perko cap screws down and clicks just like your car does.
    And you do not need to use a charcoal cannister.
    And less of a problem with a fuel spill when refilling as no vent exists to leak fuel over the side.
    I do use an old bathroom towel around the fill when refueling.

    I also put in a Perko one way fill valve in the fill pipe. Prevents say if the boat is moving and your refueling, the fuel from welling back up and geysering out of the fuel fill.
    But its not really needed.
    The big advantage of all this, the fuel stays fresh a very long time, it is basically sealed from the atmosphere most of the time, so for me this E10 fuel is not the big problem it used to be for me, with stale fuel and constant bad carb issues. And I dont buy fuel stabilizer anymore, so it saved me that cost too.

    My experience has been real positive doing this. And rather than any fuel tank pressure, it seems to have a very slight vacuum in the tank instead.

  15. #15
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    Jun 2000
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    Madison Wisconsin
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    Default Re: Non-vented fuel tank - leaking?

    I recently replaced the old Yamaha metal tank on the Whaler with a six gallon plastic Attwood tank. They warn you right on the tank that it will expand, but that sucker blows up like a balloon in the hot sun - to the point where the bottom gets round and it no longer sits flat. No leaks yet, but it certainly got my attention and motivated me to check over all the fittings and the hose carefully.

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