I've always understood that the auto-stop feature was built into the fuel-filler nozzel rather than the tank you are filling.

If this only happens at this one station, I would complain to the manager or the Bureau of Weights and Measures.

If this happens at every gas station, I would make a trip to the dealer. The back-pressure is not building sufficiently to trigger the auto-stop of the pump.

I may be way off base here, but this is the way I have always understood these pumps to work.

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William
76 240D (W115) - 550K miles
78 300D (W123) - 200K+ miles