Cessna 150 fuel vent issue

Discussion in 'Maintenance Bay' started by n20junkie, Jun 20, 2008.

  1. n20junkie

    n20junkie Pre-takeoff checklist

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    Grant Farmer
    I have a 150L, 73' that has been slowley dripping fuel after top offs. Now after sitting for a few months its worse. I have to open the tank to check the orientation of the vent valve, and would just rather replace it. Does anyone know the fitting size for the vent valve. I assume its either -4an or -6an by looking at the manual. Thanks.
    Grant
     
  2. Dan Thomas

    Dan Thomas En-Route

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    Can't stop that drip. The vent is just that: a vent, with a check valve to let air in easily but out slowly. Park the airplane on a level spot. If you park it left wing low you'll lose fuel. Sitting in the sun the fuel will expand and leak out, too. Maybe don't fill it quite so full if you're not going anywhere right away.
    Cessna singles do this. So do lots of other small airplanes using underwing vents, especially high-wing airplanes that have little dihedral. We run six of them and I won't allow any airplane with full tanks inside the hangar, because the fuel will sooner or later end up on the floor and present an awesome fire hazard.

    Dan
    ________
    XT660
     
    Last edited: Jan 19, 2011
  3. ghopp

    ghopp Filing Flight Plan

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    This topic has been discussed ad nauseum on the cessna150152.com site, lots of good information over there but can be difficult to find. I have a friend with a similar vintage 150 that had a terrible leak but he fixed it. It does not leak now. My 67G used to leak some, but not a lot. It has to do with ensuring the vent tube is in the correct orientation, it's easy to get it wrong.

    If you are not getting into your wing tanks for maintenance, use Dan's suggestion to find a level surface, then put the left wing (main gear) up on a 2x4 to raise its height.
     
  4. KennyFlys

    KennyFlys Guest

    Our 1976 M-model leaks some but we no longer allow it to be topped off. Fuel is added for each flight as required due to weight concerns.
     
  5. Ddayle

    Ddayle Line Up and Wait

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    You mean it is not normal? both our club 150's (67's) do it. In fact the asphalt under the vents is crumling from constant exposure to fuel. DaveR
     
  6. ntbjounin

    ntbjounin Pre-takeoff checklist

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    just about every light cessna single ive flown has had that problem, EXCEPT ONE! It always puzzled me actually. It was kept in a t hangar and kept in amazing condition! But how that keeps it from leaking still baffles me.
     
  7. Dan Thomas

    Dan Thomas En-Route

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    OK, here's the deal. I had to go look it up in both the 150 and 172 manuals. Some airplanes will leak worse than others, and here's why:

    The vent valve is inside the tank. It appears to have a small hinge on the check valve, and this hinge must be at the top. The valve assembly is screwed onto a piece of tubing that has two bends to position the valve higher than the tube's entry point into the tank, so that the valve will be as high as possible in the tank. If this thing gets turned when the mechanic tightens the external vent tube nut, the valve will dip down into the fuel. With both caps on, the vapor pressure of the fuel alone will push fuel out of the vent, rather than vapor, because the vent's opening is submerged in fuel. Get the picture?
    Of course, really full tanks in an airplane that's sitting left wing low will still lose fuel.

    Dan
    ________
    herbal vaporizer
     
    Last edited: Jan 19, 2011
  8. n20junkie

    n20junkie Pre-takeoff checklist

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    Grant Farmer
    Thanks Dan, thats pretty much the opinion I keep getting on the deal. Maybe this winter I will pull the tank and check it out. I need her to fly this summer, so that will have to wait.
     
  9. LDJones

    LDJones Touchdown! Greaser!

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    Sorry for the necropost, but am dealing with this issue in a friend's 150 and am wondering if anyone has tried this solution:

    http://www.mcfarlaneaviation.com/Details.aspx?Article=288

    Thanks in advance.
     
  10. flyingmoose

    flyingmoose Pattern Altitude

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    Will be interesting to see if anyone has had luck with this. Seems like it could work.
     
  11. Witmo

    Witmo Pattern Altitude

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    I've installed this on an A150L that would leak a lot of gas if filled to the brim. After the install, it doesn't leak a drop unless you have it filled to the brim and make a sharp turn while taxiing or being towed. It will then drip a little for a short time until the fuel stops sloshiing, Compared to before the installation, we have had to have saved hundreds of dollars in wasted fuel. In other words, well worth it.
     
  12. n20junkie

    n20junkie Pre-takeoff checklist

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    I just had that tank open too :( guess I will buy this and try to fix that damn leak!