Gas Tank Overflow Problem

There never were "flappers" that had to do with nozzle shutoff. It's cause by a pressure surge coming back up the fill pipe. If you have an earlier car with a "leaded" (larger dia.) filler, the new smaller nozzles may not shut off.

Most of this is poor design, adjustment, and installation. Some stations around here operate at very high pressure compared with others to hasten fill time. They also don't shut off as reliably. The fillers on my (dual tanks) old 86 ranger are at about the same height as my Dart, and some of them don't even shut off in the Ranger without spilling.

Yup. I guess jam 'er up with towels, or else pick and choose your station.