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Fuel tank question....

Discussion in 'A4/S4 forum(B5 Chassis)' started by Izzy1, Dec 16, 2009.

  1. Izzy1
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    Izzy1 Vorsprung Durch Technik

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    [Dec 16, 2009]
    hi guys,
    i'm hoping this is a simple question.
    was filling up my car last night and i always fill to the brim. i noticed a little button thing on the left of the opening. what is it? and what does it do?

    cause when i hit it by accident it seemed to suck my fuel through... allowing me to put more fuel in the tank.

    if anyone can shed some light on this i'd be greatful.
    #1
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  3. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator VCDS Map User

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    [Dec 16, 2009]
    Thats the centeral locking pin. When the car is locked so is the cap
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  4. Izzy1
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    Izzy1 Vorsprung Durch Technik

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    [Dec 16, 2009]
    when i pressed it, it was taking in air. made an air intake noise. if you know what i mean.
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  5. denzelburner
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    denzelburner Member

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    [Dec 16, 2009]
    [FONT=&quot]The little button is the thing that vents your fuel tank of air when you put the fuel filler cap back on. As you screw it in, it presses it down and vents.
    It seems to suck your fuel in, as it is replacing the space the air was taking up at the top of the fuel tank. This only happens if you are filling it right up, otherwise there is sufficient space in the tank for both the fuel and air, until the fuel tank pressure has built up enough for the fuel to work it's way up the filler neck. the fuel in the neck then replaces the air when the vent returns the tank to a more atmospheric pressure, hence how you can put 'extra' fuel in.

    Hope i'm not teaching you how to suck eggs, and it explains this useful [/FONT] [FONT=&quot]phenomenon[/FONT] :happy:
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  6. Izzy1
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    Izzy1 Vorsprung Durch Technik

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    [Dec 16, 2009]
    and as simple as that he knew what that "button" was for. lol

    thanks.
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  7. denzelburner
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    denzelburner Member

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    [Dec 16, 2009]
    No worries
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  8. jcb
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    jcb Active Member VCDS Map User

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    [Dec 16, 2009]
    oo oo, a new toy to play with on my car.
    learn something new everyday
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