Pumping Gas / Shut Off Question

Discussion in 'Dodge Challenger General Discussions' started by synoptic12, Oct 21, 2021.

  1. Yes

    5 vote(s)
    62.5%
  2. No

    3 vote(s)
    37.5%
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  1. synoptic12

    synoptic12 Full Access Member

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    Looking for information regarding the shut off process. Should the lever be fully depressed for the shut-off to work. All replies are appreciated.
     
  2. SRT-Tom

    SRT-Tom Well-Known Member Staff Member Super Moderator Article Writer

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    When you fill up your gas tank, you squeeze and lock the pump handle to the on position. When your tank is full, it automatically "clicks" and shuts off the fuel. If you want to "top off" and round out the cost (e.g., $30.85 to $31.00), you can manually squeeze the pump handle a few quick times, being careful not to overfill.

    This is how the pump works. Near the tip of the nozzle is a small tube that leads back to an air diaphragm in the handle of the pump. When you first start pumping gas, the diaphragm is all puffed up and inflated, and air is flowing through the small tube. Once the tip of the nozzle gets submerged in gas (as the tank is filling up), gas starts getting sucked up into that little tube. When the little tube gets full of gas (which, remember, is more dense than air), there is a pressure change in the pipe. Suddenly, in an attempt to even out the pressure, the air from the diaphragm gets sucked down and out of the pipe. Once the diaphragm decreases in size, it triggers the automatic shutoff within the nozzle.

    An easy at home way to see the Venturi Effect is with a drinking straw. Think of what happens when you suck on a straw that's not in a liquid. The air flows through just fine- this is what the little tube inside the nozzle looks like when you first start pumping gas. Now cover the end of the straw. The straw starts to collapse as a vacuum is formed- this is what happens when the gas covers and starts getting pulled into the small pipe. Its that vacuum that forms that pulls the air out of the diaphragm in the nozzle and triggers the automatic shutoff.

    That's all it is. No diodes, no sensors, no magic wands. Just a little pressure change and a whole lot of science.
     
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  3. synoptic12

    synoptic12 Full Access Member

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    Well, thank you for the information. However, I experienced an issue while refueling at a Mobil service station. Upon filling the tank, I kept the nozzle lever depressed halfway. When the tank was full, the 'shut off' did not work as gasoline spilled out over the side of the vehicle. I called Mobil and said the shut off was not working properly. The manager said the lever 'has to be fully depressed' for the shut off to operate properly. I've never heard of this before. However, Mobil is compensating me for the issue. can you refer or reply to this specific aspect.
     
  4. NC20RT

    NC20RT Full Access Member

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    For me I just try to hit one of those 'grooves' that locks in the flow and lets the pump do it's thing. It does NOT work at every station and I have found that different parts of the country have different pumps or tolerances.

    We generally travel nationwide in our GT/CS and in the northeast part of the country it can be a bear to fill up the tank normally and you have to manually do so. In NJ I had to have an attendant help me until I learned to hold the handle 'upside-down' to get the fuel to flow. I ran into that a few times up there and in upstate NY too. When we took our Trans Am to Cape Cod a few years back we had a an 'upside down' moment at an Exxon station in MA. At least I remembered the trick. Crazy stuff! Normally elsewhere the pumps work with the automatic shut-off. Seeing that you are in FL, there should be no problems. We lived there our entire lives until moving to NC about 20 years ago.

    I have never had an issue with the Challenger but I've only driven 3,000 miles so far and just here in the southeast.
     
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  5. synoptic12

    synoptic12 Full Access Member

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    I've experienced those issues in N.J., so I know what you're speaking about. I had no need to start litigation seeing that Mobil is compensating me. So, is the Mobil spokesman wrong when he said, "You must depress the lever fully' for the shut off to work properly? I never really use those interlocking groves set at various intervals. The Mobil spokesman made no mention of the interlocking mechanism to control the flow.
     
  6. NC20RT

    NC20RT Full Access Member

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    ^^^ Personally I never squeeze the nozzle that hard or fully open. I can't speak for the Mobil guy but that is not how I fill my tanks. It's like asking for overflows or even simple splash back on your hands.
    SLOW & EASY, like I used to do with my dates trying to get to 2nd base. :love51:
     
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  7. SRT-Tom

    SRT-Tom Well-Known Member Staff Member Super Moderator Article Writer

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    The manager was correct. You should depress the pump handle fully until you hear it click- don't hold it half way. Then, the automatic shut-off should work.

    After it shuts off and if you want to squeeze a little more gasoline into your tank, squeeze the pump handle quickly on and off.
     
  8. SRT-Tom

    SRT-Tom Well-Known Member Staff Member Super Moderator Article Writer

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    How do you pump your own gas? Attendants are required to do it in NJ.
     
  9. 70-426_10-SRT

    70-426_10-SRT B&E body lover

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    It's funny, here in Oregon they don't let us pump our own gas either
    except for diesel or motorcycles.

    I use the same Chevron Station for 90% of my gas.
    The guys know me, and we always talk cars.
    Only TWO of there pump work correctly and the manager swares all are the same.
    But if I don't get those two pump, they have to turn the nozzle upside down.
     
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  10. B5blueRT

    B5blueRT Full Access Member

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    I never ran into a situation of turning the nozzle upside down, this is the first time I read about it.
    All the stations by me have a cover over the nozzle to help stop fuel overflows from splashing out on the quarter panel. I have found that (as Tom mentioned) the auto shutoff works about 99% of the time when the nozzle is fully depressed. I have more trouble and overflow issues back when trying to fill up slowly. I believe that the nozzle senses the pressure more reliably with a faster fill. I can hear the gas starting to come up the fill tube and then the nozzle clicks off. And yes, you can usually add more fuel to top it off if you want. Hate to admit how many times I had filled slowly and the gas started pouring out of the fill tube, the shut off never activated and I couldn't hear the gas coming up the fill tube.
    BTW: you shouldn't top off the tank. The gas will fill the vent tube and over time cause the vent solenoid to become defective.