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What're all those small hoses for on poly gas tank??

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by ErikH, Mar 10, 2003.

  1. ErikH

    ErikH 1/2 ton status

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    What\'re all those small hoses for on poly gas tank??

    I'm in the process of replacing the sending unit on my poly gas tank (poorly installed by previous owner), and I was wondering what all the smaller hoses were for... They seem to lead to strange places and I want to make sure water doesn't find its way into my tank again. Can I plug anyone of them up? Thanks for any help
    -Erik
     
  2. Roostr84

    Roostr84 1/2 ton status

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    Re: What\'re all those small hoses for on poly gas tank??

    How many do you have? My guess would be a vent/ evaporation line and maybe a return line for a fuel injection conversion.
     
  3. Steve_Chin

    Steve_Chin 1/2 ton status

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    Re: What\'re all those small hoses for on poly gas tank??

    Vent/evaporative stuff is my bet. My 40 gallon tank has three vent tubes, one return tube, the pickup tube, and the filler tube.

    Do *NOT* plug the vent tubes. Doing so will give you tuning fits. Hook them up correctly to the liquid/vapor separator and ensure that the liquid/vapor separator is correctly hooked up to the charcoal canister.
     
  4. Triaged

    Triaged 1/2 ton status

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    Re: What\'re all those small hoses for on poly gas tank??

    Mine has a bunch too. I haven't counted them all but there are about 3 that go up the tube by the fuel filler (no idea what for?), and a few that go to the (now non-existant) carbon canister. I bet there are a bunch you can cap off! Just make sure you leave at least one vent line.
     
  5. 70~K5

    70~K5 1/2 ton status

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    Re: What\'re all those small hoses for on poly gas tank??

    As long as you're running a vented gas cap, and that's the big IF, why do you need ther extra vent on the tank? /forums/images/graemlins/confused.gif
     
  6. TED

    TED Registered Member

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    Re: What\'re all those small hoses for on poly gas tank??

    I plugged all but the fuel line and one vent line on my poly tank.
     
  7. LKJR

    LKJR 1/2 ton status

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    Re: What\'re all those small hoses for on poly gas tank??

    there is one vent that goes next to the filler, that's so your tank can breathe when you fill up otherwise it would burp on ya, one is the pickup, and the other is probably a return.
     
  8. ErikH

    ErikH 1/2 ton status

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    Re: What\'re all those small hoses for on poly gas tank??

    Please tell me more about this canister and water separator... Which line(s) go to the canister (which I removed, oops), and what's the proper hookup. I have a 21-gal poly tank with three connectors (one larger for the return and two others -- one goes to the mystery riser behind the left fender; and the last line goes somewhere... maybe to the non-existent canister???). Thanks for your help!
    Erik

    [ QUOTE ]
    Do *NOT* plug the vent tubes. Doing so will give you tuning fits. Hook them up correctly to the liquid/vapor separator and ensure that the liquid/vapor separator is correctly hooked up to the charcoal canister.

    [/ QUOTE ]
     
  9. Steve_Chin

    Steve_Chin 1/2 ton status

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    Re: What\'re all those small hoses for on poly gas tank??

    There shoul;d be a minimum of three vent lines. One bigger one that goes to the top of the filler neck, and two smaller ones that route from either side of the fuel tank to the liquid/vapor separator (the "tube thing" behind the filler neck). The reason that there are two vent lines attached to the liquid/vapor separator (I'll call it the standpipe from here on out) is because a submerged vent line does not vent well enough (it's basically hydrostatically locked). If the truck has a nearly full tank and is tilted to one side, the opposite vent tube is functional and will allow air into the tank as the fuel pump pulls fuel out of the tank.

    The charcoal canister is a pretty simple filtration device that separates unwanted fuel vapors out of the air that is expelled from the tank (and in some models the carburetor). Those vapors are collected for ingestion into the engine when it is running. It does not a thing to hurt performance and can help make a steel gas tank and steel fuel lines last much longer because it also filters moisture out of the air that is vented into the tank.
     
  10. ErikH

    ErikH 1/2 ton status

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    Re: What\'re all those small hoses for on poly gas tank??

    Ah ha! But wait... You say two of the three lines go to the standpipe and the third goes to the top of the filler neck. Sounds logical, BUT which line feeds the canister up front?? Is there a "T" somehwere in one of the two smaller vent lines? Again, thanks for the help!

    -Erik

    [ QUOTE ]
    There shoul;d be a minimum of three vent lines. One bigger one that goes to the top of the filler neck, <font color="blue"> and two smaller ones that route from either side of the fuel tank to the liquid/vapor separator (the "tube thing" behind the filler neck)</font>. The reason that there are two vent lines attached to the liquid/vapor separator (I'll call it the standpipe from here on out) is because a submerged vent line does not vent well enough (it's basically hydrostatically locked). If the truck has a nearly full tank and is tilted to one side, the opposite vent tube is functional and will allow air into the tank as the fuel pump pulls fuel out of the tank.

    The charcoal canister is a pretty simple filtration device that separates unwanted fuel vapors out of the air that is expelled from the tank (and in some models the carburetor). Those vapors are collected for ingestion into the engine when it is running. It does not a thing to hurt performance and can help make a steel gas tank and steel fuel lines last much longer because it also filters moisture out of the air that is vented into the tank.

    [/ QUOTE ]
     
  11. Steve_Chin

    Steve_Chin 1/2 ton status

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    Re: What\'re all those small hoses for on poly gas tank??

    Nope... The standpipe has three nipples. Two lead to the fuel tank vents, the third leads to the evaporative canister.
     

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