Fuel cap air pressure

Whenever I open my passenger-side wing fuel cap on my 1961 Cessna 182D, I feel and hear and big rush of air coming out. I'm worried the tank is creating a vacuum that could disrupt fuel flow. Has anybody experienced this before?

Comments

  • If it were a vacuum you'd have a heck of a time getting the fuel cap off. I would advise checking ALL the vents for your fuel system.

  • Scott ShererScott Sherer COO Forum Moderator

    I concur!

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Cessna Owners Organization Forum Moderator and Cessna Owners Author.

    Need help? Let me know!

  • "I feel and hear and big rush of air coming out."
    Just to confirm Hill, it's vacuum and not pressure in the fuel tank?
    If vacuum, is it both Tanks showing this vacuum? My thoughts are it developed because of a blockage in your forward facing vent tube (on the left wing placed behind the Wing Strut joint on my 182A) AND the vents on both fuel caps are blocked, a pretty rare occurrence. My plane has a crossover vent tube connecting both Bladder Tanks together. More clues where the blockage might be; if there's an uneven fuel tank burn or just the RH tank sucks air when removing it's Tank Cap.
    Where ever it is, you've got to clear up that vent system before you take that back plane up in the air. A collapsing bladder does not count as a venting solution and you don't want to be forced to make an unscheduled engine-out landing because of fuel starvation. Would be wise to get an A&P involved and Logbook entries made. They're schooled to fix these problems, and this is a serious one.

    Steve

  • Hello, new to the Cessna forum having just purchased a 1975 C182. I am having the issue where fuel is primarily being drawn from the left tank even though the selector is set to both. I'll have to check next time I fuel to see if there is a vacuum on the tank as mentioned above. I have run the plane on the right for maybe 10-15 minutes within gliding range of an airport and didn't have an issue. But I just did a one hour flight this week, used 11 gallons, 10.6 went into the left tank, 0.4 on the right. That does not seem right to me. I am looking for suggestions on where should I direct my attention to resolve this?

  • Scott ShererScott Sherer COO Forum Moderator

    The Skylane service manual should have service instructions for aligning your underwing vents and also for how to check your vent lines. Vent positioning tolerance is +/- .03" from specification.

    See pages 12-10 and 12-11 here. It's exactly the same as in my Skywagon manual. Or find the appropriate service manual if this one doesn't apply to your model. http://www.redskyventures.org/doc/c...s/Cessna_182&Skylane_1969-1976_D2006-4-13.pdf

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Cessna Owners Organization Forum Moderator and Cessna Owners Author.

    Need help? Let me know!

  • Scott ShererScott Sherer COO Forum Moderator

    Owned a Lane for years and hung around with other Lane owners. Yeah, vent tube position, caps (leaking gaskets), mud daubers in the vent (mine), and flying around on both, are all likely suspects. The lines from the fuel pump to each side are not the same total length and along with minute differences in air pressure across the wing span can result in differential fuel level.

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Cessna Owners Organization Forum Moderator and Cessna Owners Author.

    Need help? Let me know!

  • Scott ShererScott Sherer COO Forum Moderator

    I ran across this while researching your problem: For a reference, this is verbatim from the 182P Owner's Manual fuel system section (without the diagram).

    "FUEL SYSTEM.

    Fuel is supplied to the engine from two tanks, one in each wing. With

    the fuel selector valve on BOTH, the total usable fuel for all flight conoutlet,

    ditions is 60 gallons for the standard tanks.

    Fuel from each wing tank flows by gravity to a selector valve. Depletely

    pending upon the setting of the selector valve, fuel from the left, right,

    or both tanks flows through a fuel strainer and carburetor to the engine

    induction system.

    The fuel selector valve should be in the BOTH position for take-off,

    climb, landing, and maneuvers that involve prolonged slips or skids.

    Operation from either LEFT or RIGHT tank is reserved for cruising

    flight.

    NOTE When the fuel selector valve handle is in the BOTH

    position in cruising flight, unequal fuel flow from each

    tank may occur if the wings are not maintained exactly

    level. Resulting wing heaviness can be alleviated

    gradually by turning the selector valve handle to the

    tank in the "heavy" wing.

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Cessna Owners Organization Forum Moderator and Cessna Owners Author.

    Need help? Let me know!

  • Thanks everyone for the help. I am leaning towards the vent alignment after looking at the service manual drawings, I'll measure it this weekend but I seem to remember during preflight that the tube definitely leans inboard of the strut by more than the prescribed amount. Again, I appreciate the quick help on this.

  • Scott ShererScott Sherer COO Forum Moderator

    Good luck and let us know how it turns out :)

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Cessna Owners Organization Forum Moderator and Cessna Owners Author.

    Need help? Let me know!

  • If a vent tube is not in the "dead air" zone behind the strut, it will pressurize the tank on that side and gas will flow out of that tank before the other. If you happen to find yourself in icing conditions, the mis-positioned vent can ice up, preventing venting and cause loss of fuel flow due to the tank not being vented. Though if you pick up that much ice a little fuel flow problem likely won't be your primary concern.
    It took me a couple tries to get our vent tubes properly located so that fuel feeds evenly. The positional tolerance is rather small. Note that if you fly out of rudder trim (ball not centered) fuel will never feed evenly.

  • I have had my 1973 P for over twenty years. When I purchased it the right tank did not draw fuel very well, it turn out the cross over vent line had about 6” of mud daubers restricting the line. I found a coax cable that fit through & pushed them out. I will still use more fuel out of the left tank due to only having a single vent on the left side. Cessna latter went to two fuel vents. On longer cruses I will switch the fuel selected to the right tank to equal out the fuel in my long range bladder tanks. I would check out the cross over vent line before trying to realign the vent inlet behind the strut.
    Good luck.

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