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Thread: Gas pump auto shut off question

Forum to discuss Austin Healey Sports Cars

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    Gas pump auto shut off question

    When filling up the gas tank on my Healey the gas pump auto shut off doesn't seem to work. This results in some gas spilling out over the trunk area. Can't figure out why this occurs as even filling up a gas can will cause these pumps to shut down when full. I have a standard Healey gas tank, neck and cap. Any idea why this happens or what I can do to prevent it?

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    Jedi Warrior roscoe's Avatar
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    Re: Gas pump auto shut off question

    The auto shutoff on gas filler nozzles depend on a venturi in the gas flow path and a sensing line that ends just inside the end of the nozzle. The venturi creates a bit of a vacuum as the gas flows through it and it causes a small stream of air to be sucked up the sensing line. As long as the fuel doesn't reach the end of the sense line a diaphram controlled shutoff valve allows the gas to flow. As soon as the nozzle tip is immersed in the rising gasoline the diaphram valve cuts off the gas flow due to the change in pressure in the sense line due to it pulling gas instead of air.

    If that system doesn't work for your Healey it can only be because the fuel level rises in the filler neck and the nozzle is at such an angle or position that the sense line tip isn't being immersed. I'll bet if you carefully fill the tank and slow down, maybe way down, before the fuel rises into the narrow neck of the tank, that the shut off will work. Also, if you look into the tip of the nozzle and see where the sense line is you may be able to better position it so it sees gas earlier as it rises in the filler neck. Even knowing this and trying to make it work I put a towel around the base of my filler because it is in the boot (BN2) and I dont like gas seeping around.
    Jon Robbins
    1956BN-2 (do it all yourself, you'll be glad you did)

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    Re: Gas pump auto shut off question

    Mine does the same thing. I think it's because the filler neck is so long and the top of the tank is flat. The displaced air has nowhere to go when the tank reaches the full level, and the fuel is coming in so fast it blows out before the nozzle can react. Anyway, I watch the pump gauge and when I get near the full state I slow the pump down and can usually get more fuel in the tank without the blow back.
    AJ

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