Boiling, bubbling gasoline?! In tank??

Fuel and Air Systems

  1. WM23M9

    WM23M9 FBBO Gold Member FBBO Gold Member

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    OK, What in the world, causes gasoline to bubble or boil in the tank?! Running Non-Ethanol, with a bit of "Race Gas" 105 octane.. 440 Six Pack car. Drove a bit yesterday, 70° outside temp, engine temp SHOULD be 190°-195° for a 6 pack I know, however, I'm temporarily running a 180° thermostat. Mechanical pump. No return line. Never had this happen before, In YEARS of driving it.
    Had gas pouring out of the fuel lines near the tank, seems to be when parked. Cannot confirm its coming from Filler Tube, seems dry. Just had new sending unit installed. Did notice 2 of the short rubber "Go Nowhere/Vent lines"? on the tank were loose.
    Could have been the problem. But its INTERMITTENT. Only pours gas out when driving, like from 2 spots, about 11" apart. And stops when I park to check it?
    Weird! Will try again today, maybe the 3 HOSE CLAMPS I installed last night helped?
     
  2. Beekeeper

    Beekeeper FBBO Gold Member FBBO Gold Member

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    Is this the car in your avatar? if so have you check your fuel cap and filler neck grommet?
     
  3. Don Frelier

    Don Frelier FBBO Gold Member FBBO Gold Member

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    Remember you've got hot air flowing under the car when driving so you will be heating the tank.
    Check the sending unit new seal and lock rings have a history of being too sloppy.
    Check clamps.
    Vented cap?
     
  4. Brewzer67

    Brewzer67 Well-Known Member

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    If you just changed the sending unit, what lock ring did you use? If you used the new one I would switch back to the OEM one. The repro ones tend to be a little thinner and frequently leak.
     
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    • moparedtn

      moparedtn Ed on the Ridge FBBO Gold Member

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      Ethanol-poisoned fuel these days eats right through the old type fuel line.
      If you have older fuel lines down there, it could be that.
      When you fetch replacement fuel line, make darn sure you get the right type -
      I think around here it's designated "fuel injection" fuel line or "safe for ethanol"
      right on it.
       
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      • Lionized

        Lionized Well-Known Member

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        Tank vent blocked?
        Does the tank hiss/contract when you remove the cap?
         
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        • Ranger16

          Ranger16 Well-Known Member

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          Yeah that ^^^^

          Remember, vacuum lowers the boiling point.
          That said, I've never heard of fuel "boiling" in the tank.
           
          Last edited: Mar 5, 2021
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          • WM23M9

            WM23M9 FBBO Gold Member FBBO Gold Member

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            Turns out, it was coming from a vent line that went, Nowhere. There are 2, one that was leaking, has been on there forever. Has a 2" hose & "ZigZaging 1/4" steel line that just ends. Doesnt appear to leak from the lock ring. No vented cap. Never did this till replaced sending unit. Of course I didnt replace it personally. Had a shop do it while had some paint work done. I ummm, blocked it by using a short hose, 2 clamps & a bolt in one end. Pretty sure tank's supposed to be vented.
            Yeah the filler tube just kinda sits in the damn tank, that rubber grommet needs R&R..
            Stopped leaking, but will need get manual out and try figure out why that strange line is leaking. I guess a pic or 2 would help..lol Been a long week with this car.
            Much appreciate the help!!
            Thanks!
             
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            • R/T

              R/T Well-Known Member

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              Same happened to me ,muffler shop refused to install H pipe because of fuel Leak! Turns out Abraham at the parts store sold me the wrong size hi- pressure fuel clamp. Should have gone with the old style hose clamp! The longer vent line leaked at the tank nipple.
               
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              • Kern Dog

                Kern Dog FBBO Gold Member FBBO Gold Member

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                The boiling point of gasoline ranges between 104 and 392 degrees Fahrenheit. The wide range of boiling points is due to the many different blends of components available to provide different characteristics such as higher octane, lower fuel deposits and overall volatility.
                 
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                • moparedtn

                  moparedtn Ed on the Ridge FBBO Gold Member

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                  The vents on your tank actually do sort of "go nowhere" - they're exposed to atmosphere,
                  hence why they're vents. They ought to look like this:
                  3748023-DSCN273628Custom29_zpsbf24cbe3.jpg
                  Notice the grommets on the longer one - those are for where that vent passes up into the trunk, then
                  back down out of it.
                  I even have a vented gas cap on mine, even though I suppose it's not necessary.
                   
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                  • WM23M9

                    WM23M9 FBBO Gold Member FBBO Gold Member

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                    Yep. Looks like the "Leaker"!
                    Never had gas coming from it. However, my vent tube comes FROM the sending unit assembly! Only 1 other line coming from LH side of tank. Runs up into trunk. I had to clamp off the vent to stop the leak. Nothing seemingly coming from filler neck OR lock ring. All from this tube. I DID have 105 Octane race gas in it for a while. Always run Non-Ethanol. Tricky place to get into without a lift!
                    20210305_094708.jpg 20210305_094454.jpg 20210305_102806.jpg 20210305_094103.jpg 20210305_094103.jpg
                     
                  • dadsbee

                    dadsbee FBBO Gold Member FBBO Gold Member

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                    Well that explains fuel everywhere, that is NOT boiling, it's just leaking. Who put the sender in and why did they hook a vent line to what is supposed to be the return line port on the sender. That and even being installed in the wrong place looks like they left a clamp off the joiner hose..
                     
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                    • ckessel

                      ckessel Well-Known Member

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                      Fuels are blended for the climate conditions. You might have picked up a load that reflected your balmy weather of the last couple of weeks. Colder temps the fuel has a lower boiling point and opposite for hot.
                       
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