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  1. #1

    Default Gas tank air lock

    Can anyone advise me what I can do to make my trip to the cas pumps a biy easier? It seems when I attempt to fill my POLAR SKIFF It takes forever because of an apparent air lock or vent issue. I can get in 5-6 gallons then have to trailer it around for awhile to clear the line.The vent works. Any ideas?? Thanks so much

  2. #2
    Chief Petty Officer Bob's Garage's Avatar
    Join Date
    Apr 2008
    Lakeland Florida

    Default Re: Gas tank air lock

    There are only 2 reasons (that I can think of) that would cause a slow or no fill of a built in fuel tank.
    • Non-working vent
    • Non-working fill hose

    Even if the vent is "working" it may have a tight bend, or crimp, that reduces the flow of air from the tank when it is being filled. The out rushing of air must be at it's maximum to allow fuel to displace it in the tank at the speed it is being pumped in. This is not the same as the amount of air required to allow the engine to run, which removes the fuel at a much slower rate.

    A non-working fill hose would be much easier to diagnose as you would have fuel everywhere if it leaked, was disconnected, or if it was kinked.

    So my suggestion would be to check out your vent line. From the tank it should run unobstructed to the 90degree overhead bend at the vent thru hull.

    To check the hose I would remove the hose (tie a cord to the hose so you can pull it back), inspect it visually, and use a compressor to blow out the inside, there may be an obstruction in it.

    The hose needs to be class "A" or "B" fuel hose, rubber, and probably 5/8" diameter.

    Also check the fitting at the tank for obstruction and that the thru hull vent is not obstructed. To do this I would remove both for a visual inspection.

    I realize this is a lot of work, and may require some adaptation on your part, but it is what I would do if nothing was obviously wrong.

    My bet is a crimp in the hose.

    You will now receive other, possibly better, ideas.

    Have fun.

    One last thing, you don't mention your fuel tank capacity. I am assuming it is more than 5 - 6 gals?
    Member and Boat Safety Instructor with the Lakeland Sail and Power Squadron;

  3. #3

    Default Re: Gas tank air lock

    Thank you Bobs Garage. I appreciate it

  4. #4
    Commander NHGuy's Avatar
    Join Date
    May 2009
    Nashua, NH

    Default Re: Gas tank air lock

    I have a little-bit-slow fill hose on mine. It is around 2" diameter fill hose, and the vent is quite a bit smaller as stated above. My fill hose makes a contorted S getting to the tank, since the longest part of the hose is nearly horizontal that is the (believed) cause of the slowup. If I'm at a gas pump they can only use the medium pump speed.
    I think you have a more pronounced issue and I'd suggest pulling the fill & vent hoses plus the vent fixture for inspection. Replace the hoses with marine fuel line or somehow clean them all up. While things are apart get a good look in the fuel fill on the tank and make sure there are no obstructions. You can also pull the sending unit to get a good look in there. The inside of the fuel tank has to be perfectly clean. If it isn't, siphon out the old fuel and then get all the junk out.
    A couple of hints when you do this. Disconnect the battery before doing any fuel system work. Work in a ventilated or outdoor spot. If the hoses need to be pulled through body cavities tie something to them as you pull them through. Makes reinstallation much easier. Run out or siphon off as much fuel as you can beforehand. Work on a trailer or lift, boat movement will drive you nuts it you need to do anything requiring precise movements.
    Use a 90 degree bent pick to free up hoses from fittings (after unclamping).
    Don't forget to replace or reinstall all wires, especially grounds to the fill and vent fittings, grounds prevent that flashing and booming that you don't ever want to see up close!
    1989 Baja Sunsport 196, Mercruiser 5.7, Alpha 1
    Moultonborough Neck, Lake Winnipesaukee, NH

  5. #5
    Moderator Bondo's Avatar
    Join Date
    Apr 2002
    The Mouth of the Chaumont River, Ny.

    Default Re: Gas tank air lock

    Ayuh,... Unfortunately, it seems Many tanks built for boats end up with the fill port, 'n the vent port,..
    Right next to each other...
    And usually on the wrong end of the tank,..
    As far as fillin', 'n ventin' purposes....

    I've seen boats that'll take fuel on the trailer, 'n Not at the gas dock, as well as Visa vi......

    You just might have 1 of 'em...
    Any Grease is Better,..... Than No Grease at All.......

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