Theory behind 2 fuel tank vents?

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  1. sprice

    sprice Member

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    Been long since I took the tank off and am now reassembling with a new tank. Same as the one that came out. I do not have the vent lines and will replace however I am not clear on the theory. One line appears to stay under the floorboard. The other rises up through the floor, turns left towards the left rear wheel, up and down. Appears one is higher than the other. not sure if the outlet is same height. My understanding is that 1968 (300) is a vented cap. Under hard throttle, the fuel would be forced perhaps, into the filler tube causing a blockage of the vented cap. Air would then need to enter the tank through one or both of the vent tubes.

    I will try and bend my own however just needing to understand the theory so I don't go too low or high or situate the lines where they could plug with debris. Also, are ends open? Restrictions? Is there a better way of venting, perhaps using canisters? Thanks.
     
  2. saforwardlook

    saforwardlook Old Man with a Hat FCBO Gold Member

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    As far as I know, even today's most advanced computer technology does not allow us to yet read others' minds. Given that your description of the arrangement in your car is incomprehensible, I will have to defer to someone else to provide a response who actually has one of these to maybe help. One line goes under the car and then one line goes up into the trunk area (I assume) and then becomes two lines or ??
    Did you ever consider asking yourself whether anyone could actually understand just what you are trying to describe when you wrote it?
     
  3. Dylan Galvin

    Dylan Galvin Active Member

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    I thought that second line you're talking about is the return line
     
  4. sprice

    sprice Member

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    I'll try with the picture from manual.

    3748023-dscn273628custom29_zpsbf24cbe3-jpg.jpg
     
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  5. 1970FuryConv

    1970FuryConv Senior Member

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    If the purpose of the vents is to let in air as your fuel level goes down, such that there's no vacuum to collapse the top of the tank, I think the 2 vents allow redundancy to be certain that air can enter as fuel leaves. I don't think the exact height or length of one or the other is critical as long as they are doing their job. (the exception being you don't want them low enough that raw fuel could pour out during a hard stop.)

    My understanding of the canisters was to prevent evaporation thru the same tubes from going directly into the atmosphere.

    Greater minds may contribute more info.
     
  6. Dylan Galvin

    Dylan Galvin Active Member

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    Well I’m wrong lol
     
  7. 1970FuryConv

    1970FuryConv Senior Member

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    I've only been wrong a 1,000,004 times. I'm sure 1,000,005 is coming soon. All right, truthfully, I've lost count.
     
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  8. HWYCRZR

    HWYCRZR Senior Member FCBO Gold Member

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    After messing with my ‘68 tank the short vent is towards the top of the tank in the rear (tube runs inside the tank)and the other vents top front. Not sure why the redundancy, unlettered is just ensuring enough air flow or if it keeps one of the lines from burping fuel when venting on a hot day.
     
  9. 70NEWYORKER

    70NEWYORKER Well-Known Member

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    Two vents so the tank can always be vented...nose up or down. This way the car can go up and down hills, unlike early phords...
     
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  10. 73Coupe

    73Coupe Senior Member

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    My tank has (4) vents that connect to a separator outside the tank. From there, one vent line goes to the charcoal canister.

    The tank internally has (4) vents so that each top corner of the tank is provided with a vent which would accommodate any situation that the tank encounters, with regards to fuel level and angle of repose.
     
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  11. sprice

    sprice Member

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    What I was missing was how the tubes are situated inside the tank. The up/down/cornering comment makes perfect sense. Thank you everybody.
     
  12. polara71

    polara71 Old Man with a Hat

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    Why not replace with parts from another 68?
     
  13. sprice

    sprice Member

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    Would do however with the minus temps coming around the corner and covid restrictions (in code Red here), seems like a one could bend and install without issue, at least temporarily. Key I think, is to keep the vent tubes above the tank and filler tube.
     
  14. HWYCRZR

    HWYCRZR Senior Member FCBO Gold Member

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    Here is the original routing for a ‘68. The short one goes straight up to the shock mount cross floor support and the long one goes up into the trunk and over to the left sidewall and then back down into the unibody open frame.
    D5BD1E36-EBB1-4E31-9187-F8CF22982259.jpeg 497014E0-1301-4584-9782-E89C71389891.jpeg
     
  15. mr. fix it

    mr. fix it Old Man with a Hat

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    Digging up this older thread.

    I'm just getting ready to add these to my Polara.
    I have replaced my trunk floor with a 65 fury & since I have a 66 Polara, there's no holes for the grommets currently
    EDIT: I do have the holes required but now have to figure out where the fuel sender wire goes :lol:

    @HWYCRZR This one photo helps with the exit but not with the entrance hole from the trunk perspective.

    Does anyone have a photo without the spare tire being mounted?

    Alternatively, does anyone have photos of a 65 vent line system?
     
    Last edited: Mar 4, 2021