My tank was running very empty (light had been on for 20 miles). Range showed 13 left. Put in 5 gallons of 100 octane. Started the car. Showed same level and same range. I couldn't believe my eyes. Put in one more gallon. Same thing. Then I decided to just fill up the rest of the tank with 91. It went up to slightly above 1/2 tank, with range showing only 175 miles while I have just put in about 17 gallons of fuel. Totally puzzled, I drove away. At the light I was staring at my needle on the fuel gauge and wondering what was going on. As I stared at it, I thought I was imagining the needle creeping up. It was! Ever so slowly, the next few minutes saw the needle creeping up very slowly. 7 minutes later, I got to my destination and the needle showed almost full tank. I think if I had left the car running for a few more minutes, it would have shown full tank.
Perhaps there is a faulty sensor for the fuel gauge, but I guess the on-board computer must use data from that gauge to calculate range also.

I guess its time to go visit my dealer.

Anybody else have had a similar problem?

 

did you turn the key all the way off or just to the ACC while you were filling up...

Pretty normal issue, I had a VW that did that, I wouldn't worry about it too much.

 

So ... the more you drive, the more your tank fills up?

I'll buy your car. For a billion dollars.

 

The key was in my pocket when I filled it up each time.

 

I know. I wish this were true...

 

This happened to me once. It freaked me out. But it has not happened since.

 

In the 996 you have to fill up above a certain point for it to register fuel. I was running low and just put in 10 bucks once to get me home as I was in a hurry. Needle didn't move.

Researched and found that unless you fill up over I think like 1/2 way the needle wont budge.

So you were just messing with it's mind perhaps and thats why it was acting goofy.

Edit* Assumed you owned a 911 from the avatar. I only speak of 996 911 experience.

 

Strangely behaving sending units in the fuel tank are one of the known gremlins of the modern 911.

 

This is totally normal. When a tank is run really low and you fill up partially the sensor will not check the pressure (or float). If you fill it completely it will take some time but will come to full chek in a ten or fifteen mile drive. This happened to the 2008 Turbo Cab yesterday on a trip to Chicago. Nothing to worry about.