Gas tank on '70 makes "woosh" sound when removing cap. Normal? - NCRS Discussion Boards

Gas tank on '70 makes "woosh" sound when removing cap. Normal?

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  • Mark E.
    Extremely Frequent Poster
    • April 1, 1993
    • 4531

    Gas tank on '70 makes "woosh" sound when removing cap. Normal?

    My '70's fuel tank made a "woosh" sound as the gas cap was removed to refuel. Is this normal?

    This was the first refuel since I replaced a locking, vented cap (which was on the car when purchased) with a STANT 10852 sealed cap. The tank never made a sound with the old vented cap. The Stant was recommended by Joe Lucia on the forum as a duplicate of the original (and visually, it looks like an original '70 cap, as per the JG).

    Does the "woosh" mean the gas tank's vent line is blocked? This car does not have NA9 (evaporative canister system).
    Mark Edmondson
    Dallas, Texas
    Texas Chapter

    1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
    1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top
  • Mike F.
    Expired
    • April 25, 2011
    • 668

    #2
    Re: Gas tank on '70 makes "woosh" sound when removing cap. Normal?

    Hi Mark,

    My 70 never makes a "woosh" and I use the original cap.

    Comment

    • Terry M.
      Beyond Control Poster
      • September 30, 1980
      • 15596

      #3
      Re: Gas tank on '70 makes "woosh" sound when removing cap. Normal?

      Originally posted by Mike Furline (53259)
      Hi Mark,

      My 70 never makes a "woosh" and I use the original cap.
      I believe mine did when I used the original cap. I haven't used it (the original cap) for years now, however.
      Terry

      Comment

      • Mark E.
        Extremely Frequent Poster
        • April 1, 1993
        • 4531

        #4
        Re: Gas tank on '70 makes "woosh" sound when removing cap. Normal?

        Thanks Mike.

        Maybe my 70's gas tank vent is not working properly?

        It was good to see you at the Chapter meet!
        Mark Edmondson
        Dallas, Texas
        Texas Chapter

        1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
        1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top

        Comment

        • Gary C.
          Frequent User
          • May 28, 2012
          • 68

          #5
          Re: Gas tank on '70 makes "woosh" sound when removing cap. Normal?

          Mark,
          The vented cap vents the tank thru the cap. There are no other openings to the atmosphere in the rest of the fuel tank unless you have the evaporative control system. If you install non-vented cap, no vent and woosh sound is air rushing into tank when you open it since fuel was extracted to the engine and no vent to allow air into tank to replace the fuel that left.

          On 70 NA9 and 71 and later , the ECS uses non-vented cap and vents fuel tank thru the canister to the engine thereby providing vent to the fuel tank and keep fuel vapors from getting into the atmosphere.

          Gary

          Comment

          • Alan S.
            Extremely Frequent Poster
            • July 31, 1989
            • 3415

            #6
            Re: Gas tank on '70 makes "woosh" sound when removing cap. Normal?

            Hi Gary,
            I thought that 70 model year gas tanks without EEC provisions still had the 'button' relief valve located near the provision for the filler neck?
            Regards'
            Alan

            71 Coupe, 350/270, 4 speed
            Mason Dixon Chapter
            Chapter Top Flight October 2011

            Comment

            • Bill L.
              Expired
              • February 1, 2004
              • 1403

              #7
              Re: Gas tank on '70 makes "woosh" sound when removing cap. Normal?

              I can confirm that 70 original tanks do indeed have the relief valve.

              Bill

              Originally posted by Alan Struck (15579)
              Hi Gary,
              I thought that 70 model year gas tanks without EEC provisions still had the 'button' relief valve located near the provision for the filler neck?
              Regards'
              Alan

              Comment

              • Mark E.
                Extremely Frequent Poster
                • April 1, 1993
                • 4531

                #8
                Re: Gas tank on '70 makes "woosh" sound when removing cap. Normal?

                Originally posted by Bill Lennox (41387)
                I can confirm that 70 original tanks do indeed have the relief valve. Bill
                How does it work? Does it open when tank vacuum reaches a certain level?

                Is there a way to test it? I imagine it's probably near impossible to reach or even see it with the tank installed.
                Mark Edmondson
                Dallas, Texas
                Texas Chapter

                1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
                1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top

                Comment

                • Duke W.
                  Beyond Control Poster
                  • January 1, 1993
                  • 15662

                  #9
                  Re: Gas tank on '70 makes "woosh" sound when removing cap. Normal?

                  Those valves, whether built into the cap or remote are typically vacuum/pressure relief, and open at something like +/- 1-2 psi, but I've never seen a spec for those early pressure relief valves used on Corvettes. Check the CSM for possible information.

                  It's typical to hear that "whooshing" sound on modern cars when refueling as consumption of fuel tends to develop vacuum in the tank, but sitting on a hot day can cause the pressure to rise above ambient.

                  Duke

                  Comment

                  • Mark E.
                    Extremely Frequent Poster
                    • April 1, 1993
                    • 4531

                    #10
                    Re: Gas tank on '70 makes "woosh" sound when removing cap. Normal?

                    Originally posted by Duke Williams (22045)
                    It's typical to hear that "whooshing" sound on modern cars when refueling as consumption of fuel tends to develop vacuum in the tank, but sitting on a hot day can cause the pressure to rise above ambient.Duke
                    I expect the woosh on modern cars with a sealed system. I'm wondering if a woosh with a '70 vented system means the vent isn't working.
                    Mark Edmondson
                    Dallas, Texas
                    Texas Chapter

                    1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
                    1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top

                    Comment

                    • Terry M.
                      Beyond Control Poster
                      • September 30, 1980
                      • 15596

                      #11
                      Re: Gas tank on '70 makes "woosh" sound when removing cap. Normal?

                      Originally posted by Mark Edmondson (22468)
                      I expect the woosh on modern cars with a sealed system. I'm wondering if a woosh with a '70 vented system means the vent isn't working.
                      I know my gas tank has that vent valve, and as I said earlier I get the "whosh" when I use the original SEALED cap. I am petty sure it is the way 1970s are supposed to work.
                      Terry

                      Comment

                      • Alan S.
                        Extremely Frequent Poster
                        • July 31, 1989
                        • 3415

                        #12
                        Re: Gas tank on '70 makes "woosh" sound when removing cap. Normal?

                        Hi,
                        Actually the button valve is near enough to the filler neck that if you flatten the rubber filler/drain boot you can see and reach it, and if your hand is small enough you can reach it's other end through the filler neck.
                        You can test it's operation that way, but of course have no sense of at what pressure it opens.
                        Regards,
                        Alan
                        71 Coupe, 350/270, 4 speed
                        Mason Dixon Chapter
                        Chapter Top Flight October 2011

                        Comment

                        • Mark E.
                          Extremely Frequent Poster
                          • April 1, 1993
                          • 4531

                          #13
                          Re: Gas tank on '70 makes "woosh" sound when removing cap. Normal?

                          Originally posted by Terry McManmon (3966)
                          I know my gas tank has that vent valve, and as I said earlier I get the "whosh" when I use the original SEALED cap. I am petty sure it is the way 1970s are supposed to work.
                          So Mike F. says his '70 L46 doesn't woosh, while Terry believes his '70 LT-1 did woosh when it had the original sealed cap installed.

                          Maybe the woosh occurs if there's vacuum but not enough to open the vent valve?
                          Mark Edmondson
                          Dallas, Texas
                          Texas Chapter

                          1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
                          1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top

                          Comment

                          • Mark E.
                            Extremely Frequent Poster
                            • April 1, 1993
                            • 4531

                            #14
                            Re: Gas tank on '70 makes "woosh" sound when removing cap. Normal?

                            Originally posted by Alan Struck (15579)
                            ... You can test its operation that way, but of course have no sense of at what pressure it opens.
                            Regards,
                            Alan
                            Alan, how are you suggesting the vent valve be tested? By pushing it back and forth from each end?
                            Mark Edmondson
                            Dallas, Texas
                            Texas Chapter

                            1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
                            1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top

                            Comment

                            • Bill L.
                              Expired
                              • February 1, 2004
                              • 1403

                              #15
                              Re: Gas tank on '70 makes "woosh" sound when removing cap. Normal?

                              Hi Mark,

                              Just a thought. L46 has a return line and LT1 does not. I do not know if this makes a difference or explains why Terry's LT1 may have made a woosh when removing the gas cap and the L46 does not. Mine is an L46 and I have not heard a woosh.


                              Bill

                              Originally posted by Mark Edmondson (22468)
                              So Mike F. says his '70 L46 doesn't woosh, while Terry believes his '70 LT-1 did woosh when it had the original sealed cap installed.

                              Maybe the woosh occurs if there's vacuum but not enough to open the vent valve?

                              Comment

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