Possible explanation of the 7/8 fuel-up issue

[unicycle]

I filled up at a new station a few days ago. When I was about to start the car, I noticed the 7/8 tank thing for the first time (in nearly 170 fill-ups). But I'd also noticed that the pump had shut off earlier than expected (I put in under 7 gal but expected over 7.5 according to my ScanGauge). So I shoved in another half gallon, and the tank gauge showed full.

Then I returned to this station yesterday. Once again, the pump shut off earlier than expected. This time I didn't add any extra gas. So I think that this issue has more to do with certain stations and their extra sensitive pumps than it has to do with our cars' small gas tanks. After all, even a difference of .8 or .9 gal could lead to a fill-up that shows up as a 7/8 tank.

Next time I'm going to a different station. We'll see what happens.

[Kermit]

I had thought about that before Uni. Not too sure.

I know when I fuel, I fuel VERY slow. I pump pretty much on the first click just enough to get the fuel going into the tank. Takes a good 2.5 minutes to pump 7 gallons. Generally I don't have the 7/8 problem with one car.

Here's something else to think about. I have 2 smarts (at least for a few more days) and one consistently reads 7/8 while the other has NEVER had the problem. I pump both at the same station, same pump. One car reads 7/8 maybe 3 out of 5 fillups, more often than it does than not.

The theory sounds extremely believable but since I have two cars that use the same pump, why does the one always read 7/8 and the other always reads full?

Wow, up to 170 fillups!! I 'm not at that yet.

[fastturb]

two smarts here, too, and both act the same. I usually give an extra blimp after the pump stops but what I found is there is a lot of swirling noise from the tank filler tube for about 60 seconds. It sounds like a toilet flushing" :woohoo
If I wait for it to calm down and then put the cap on with two clicks, I don't get 7. However, if I rush a little and put the cap on right away I'll get a 7 and then many times it will bump up to 8 after 1-10 miles. Now that I've seen the picture of the tank structure, I can really understand the toilet noise as the fuel is going down the filler and swirling around

[forestacademy]

This doesn't explain the issue folks have when they leave the station at 7/8 and 20 miles later ar now at FL

[SmartDigger]

Mine did the 7/8 then full down the road. after the flash it does not do it anymore. ( Knocking on wood) Mine seemed to get the 7/8 error when I over filled it.

[unicycle]

Yeah, my explanation doesn't account for some of the odd occurrences, like the tank that fills itself 20 miles later. That's bizarre.

As for me, I correctly predicted that when I refueled the next time, the 'missing' gallon would show up, and it did. According to my ScanGauge, I should have only needed 3.7 gal, but I filled up with 4.6! The result was that the previous tank registered as getting 54 mpg while the most recent one came in at 37! I did the math, and the two together came to 46.7, which is low for me but makes sense given the recent strong winds.

[ulflyer]

When the pump cuts off, give the car a little shake, then refill. See if that helps. If its like my cycle, it gets air blocked.

Edited to add: Big shake?

[jimvw57]

The little shake method does not work. It is better to wait 30 sec to 1 min and then top it off.

[fpage77]

If I fill up (slowest possible speed) when I have 1 bar or 2 bars on verge of going to 1 bar I get the 7/8 problem. If I fill up when I have just got 2 bars (not near to flipping to one) or more I don't get the 7/8 issue. I use the same pump at same station 80% of the time.

[jediknight36]

No matter what station, I get the 7/8ths UNLESS I keep the key in acc. When I say every time, I mean at stations that will give 9.7 with 1 gal left on the gague and ones that give me 7 and I could pump more. Doesn't matter. Even did it when I filled it so much it spilled out.