vented tank cap or not ?

Discussion in 'Street/strip 400/430/455' started by thebuick, Jul 15, 2019.

  1. thebuick

    thebuick Well-Known Member

    Hi V8 Here is my question 72/455 stock build, should I be using a vented fuel cap or not ?
     
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Depends on what year car, not the engine.
     
    Last edited: Jul 15, 2019
  3. 70 GMuscle

    70 GMuscle Plan B

    I don’t think it can hurt, only help.
    I use them.
     
  4. thebuick

    thebuick Well-Known Member

    ok 1971 car 72 455
     
  5. Doo Wop

    Doo Wop Where were you in '62?

    Vented for a '71.
     
  6. thebuick

    thebuick Well-Known Member

    ok thank you
     
  7. matt68gs400

    matt68gs400 Well-Known Member

    So it really has to do with the fuel tank that’s in it rather than the motor, correct?
     
  8. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Yes, it depends on the way the tank is vented, and that depends on the YEAR of the vehicle. My 70 takes a non vented cap. I put a vented one on. With the fuel pump I have, I figure a little extra venting can't hurt.
     
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  9. lemmy-67

    lemmy-67 Platinum Level Contributor

    Some earlier models had the gas tank filler neck real low...like mine. A vented cap would have fuel pouring on the street every time I hit the accelerator pedal. So for mine, there's a separate vent pipe which goes into the trunk to allow fuel vapors to condense & drip back down, and the cap behind the license plate is non-vented.
     
  10. ranger

    ranger Well-Known Member

    Seems to me when I put a vented cap on my '70 fuel always sloshes out of the cap under acceleration, at least when the tank is full.

    Best,

    Ranger
    Aiken, SC
     
  11. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I have a vented cap on my 70. It doesn't do that on my car.
     
    ranger likes this.
  12. ranger

    ranger Well-Known Member

    Huh. Wonder why it does on mine. It's a pretty significant amount and the filler neck does not appear distorted in any way.

    Best,
    Ranger
    Aiken, SC
     
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  13. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I have no idea. I have a 1972 gas cap on my 1970 gas tank. I figured with the CV products mechanical fuel pump I have, a little extra venting couldn't hurt. A vented fuel cap is supposed to seal like any non vented cap, it just lets air in.
     
    ranger likes this.
  14. Quick Buick

    Quick Buick Arlington Wa

    I thought a vented or non-vented Cap. Depended on the fuel lines. single or duel.. which also had to do with AC. AC car twin fuel lines. Non AC single fuel line.
     
  15. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Fuel tanks have to be vented in some way. If they weren't, you would develop a vacuum in them as fuel was pumped out. Before emissions were a concern, tanks were vented to the atmosphere. Once HC emissions became a concern, automotive engineers designed systems to capture gasoline fumes and return them to be burned in the engine. Early designs with charcoal canisters appeared in the early 70's, even before in California. Today, you have completely closed systems with purge solenoids, and canisters, and the PCM monitors fuel tank pressures.

    Vapor return lines keep fuel cooler by returning hot fuel and vapor from the fuel pump to the gas tank. A/C cars run hotter, so manufacturers designed those extra lines to fight vapor lock. They have nothing to do with venting.
     
    Last edited: Aug 14, 2019
    ranger likes this.

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