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Thread: Gas Neck O-Ring Fell Off!

  1. #26
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    Quote Originally Posted by ross1 View Post
    No, if fuel leaks you have a problem. the tank is vented to the filler and a tank in the quarter panel, should be no leaks from there, ever.
    There IS a drain in the fuel door compartment intended for rainwater. You'll need to try pretty hard to over fill it that much.
    Oh great. Just checked yes there is a smaller tank in the quarter panel with a hose connecting it to the main fuel tank.

    I've never seen a literal fuel leak, just fumes when doing a full fillup to the neck that goes away after 30 miles, I assumed it would be due to some gas spilling out the breather tube.

    I'll pull the fender cover and have a look to be sure.


    Quote Originally Posted by ross1 View Post

    alang, you have an interesting transmission in that 1990 525

    I would frankly prefer a boring transmission any day of the week. lol

  2. #27
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    Quote Originally Posted by drewusmaximus View Post
    It was fine until I noticed that o-ring on the inside of the spring loaded flap. Once I removed the o-ring, I can now smell fumes. I never smelled fumes prior to that. Very odd..

    - - - Updated - - -


    I looked under to examine the fuel tank and it's fine. I will remove the wheel well lining to inspect. It was very odd to see that o-ring sticking out when i pushed the flap open.
    ive seen tanks that looked fine from below but had leaks on top of the tank. Hard to see up there. Do you have a lot of rust on the undercarriage? Salty roads and Rust is evil on tanks. Just a thought/guessing. Cheers, George

  3. #28
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    I see you live in the northeast salty winter slush and rust are kings of evil! You said you inspected under the tank but I’ve seen tank rot on top and the weld where the filler pipe attaches to the side of the tank. Salt and rust like to set up house in those spots. Just a thought/ guessing. Cheers, George

  4. #29
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    Quote Originally Posted by chislern View Post
    I see you live in the northeast salty winter slush and rust are kings of evil! You said you inspected under the tank but I’ve seen tank rot on top and the weld where the filler pipe attaches to the side of the tank. Salt and rust like to set up house in those spots. Just a thought/ guessing. Cheers, George
    There's nothing like the Northeast! Salt, ice, Snow tires, rust, and snow! There's a little rust on the tank straps but, for me to check above the tank, I would have to drop the tank. I'll be doing that next summer when I paint the car.. Fun , fun, and or fun!

    Cheers!

  5. #30
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    At the top of the tank there's a vent hose fitting next to the opening for the fuel sending unit/pump assembly. The point where that vent fitting enters the tank is a good place to look for a rust hole. You should be able to inspect it through the service plate in the trunk floor -- no need to drop the tank.

    Another likely spot is under the bumpers that protect the tank seam from the tank straps. There are two on the seam at the front of the tank. They come off of the tank with a little persuasion, they aren't held on by glue.

    When I had my leaky tank out of my 540i, that's where I found rust holes -- just pinholes under the bumpers, but holes big enough to leak gas and produce odor. The hole at the vent fitting was larger.

  6. #31
    moroza's Avatar
    moroza is offline MORΩN ΛABIA BMW CCA Member
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    Check the convenient access panel first, of course, but if that doesn't show anything, dropping the tank isn't as big a deal as it may seem. I had mine down recently - along with the driveshaft, exhaust, rear subframe with suspension, fuel hard lines, brake lines, all heat shields, and more - and it was one of the easier parts of that project. The hardest part was undoing the factory crimp-type hose clamps. The longest part was getting the rubber boot around the filler neck to seat properly. I installed it in a cold dark carport and the worst thing I might've uttered was "hm" (compared to exhaust reinstallation, which was accompanied by a litany of unprintable creativity that would make George Carlin blush).
    Last edited by moroza; 10-21-2018 at 10:41 PM.

  7. #32
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    Quote Originally Posted by moroza View Post
    Check the convenient access panel first, of course, but if that doesn't show anything, dropping the tank isn't as big a deal as it may seem. I had mine down recently - along with the driveshaft, exhaust, rear subframe with suspension, fuel hard lines, brake lines, all heat shields, and more - and it was one of the easier parts of that project. The hardest part was undoing the factory crimp-type hose clamps. The longest part was getting the rubber boot around the filler neck to seat properly. I installed it in a cold dark carport and the worst thing I might've uttered was "hm" (compared to exhaust reinstallation, which was accompanied by a litany of unprintable creativity that would make George Carlin blush).
    Geezus!!! You are a trooper! I haven't pulled the rubber boot around the filler neck but, since that was longest part of your surgery, I'm having second thoughts on pulling it off..

  8. #33
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    Bumping this thread because I came across it in a google search when trying to figure out the purpose of a mysterious o-ring in my fuel tank. Years ago I found what I think is the same o-ring posted by OP in the bottom of the e34 540 fuel tank. I thought it was odd but never looked into what it was for. Years later I found this same green o-ring resting on the bottom of my e32 740 fuel tank when replacing the fuel pump. Again, I thought it was strange there was a random o-ring in the tank but chalked it up to probably being from a prior fuel pump assembly that was in the car or something.

    Today I was inspecting the inside of the tank on my other e32 740 and found this same green o-ring on the bottom of its tank! I highly doubt it's related to the fuel pump. It must have come from somewhere else in the tank. Any ideas?

    fuel tank o-ring.jpg

  9. #34
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    Hmmm.
    Has anyone dismantled the filler pipe? I'm now wondering if there is indeed and O-ring at the restrictor/flap for leaded fuel nozzles("lead free fuel insert").
    Last edited by ross1; 02-07-2022 at 09:03 AM.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  10. #35
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    Quote Originally Posted by ross1 View Post
    Hmmm.
    Has anyone dismantled the filler pipe? I'm now wondering if there is indeed and O-ring at the restrictor/flap for leaded fuel nozzles("lead free fuel insert").
    I see what you mean; It could be a remnant piece from the "leadfree fuel insert" (#4) that shows up on some of the E32 fuel tank diagrams, depending on build date or model:

    e32fueltank.JPG


    Either way, I highly doubt that o-ring is necessary considering my cars seem to operate perfectly fine without it.

  11. #36
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    Quote Originally Posted by m60power View Post
    I see what you mean; It could be a remnant piece from the "leadfree fuel insert" (#4) that shows up on some of the E32 fuel tank diagrams, depending on build date or model:

    e32fueltank.JPG


    Either way, I highly doubt that o-ring is necessary considering my cars seem to operate perfectly fine without it.
    I would(and did) totally dismiss it as a fluke but since others have reported this I gotta wonder. I can't conceive the need for it on the restrictor but I'm not one of those engineers potty trained at gunpoint.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

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