Thanks for that info mini-e. How about that! THAT sounds like a plausible explanation. Now I know I haven't been crazy for the last 13 years. No one ever believed me when I told them I can add an extra 5 gallons after the nozzle clicks off.
You are welcome. Good timing with your post as i had the bits in the back yard. below is what i measured regarding the filler tube. the variance in fill up amounts people experience is largely to do with the tank, with the filler tube having very little volume. in civics anyway.
"It hold 3.5 cups. 1 cup = .0625 gal. so the filler tube holds approx .22 gallons of fuel. On my car that means 8.8 miles of fuel at 40 mpg. Not as much as I thought was in there."