Mark P

Thanks for the replies, though to understand how much remains at 0, I am looking for more than just what I've experienced thus far ("filling it up at that point gets close to the spec'd tank capacity, therefore I must have been empty"). That's only true if the spec'd size is accurate for the space you're filling until you stop pumping. I'm suggesting that may not be the case, and certainly introduces the variable of when do you stop filling and thus the correlation to what is the spec applied to. I'm curious about miles people have driven past 0, or fillups of over 19.8 gallons...

I certainly have driving my prior Audi/VWs 30 miles past 0 miles.

Turns out a Q5 friend of mine has provided me with some of the exact type of info I was looking for. He ran his really low (didn't run out of gas) and filled it with 22.3 gallons. So I think this does help shed some light that there probably is ~2 gallons remaining at 0 miles.

spijun

"0 miles remaining" I drove slowly another 19 kilometers , and then I poured gasoline 74L (2.0TFSI)

Audi : Fuel tank capacity approx, liters 75

MP4.2+6.0

1. If the gas nozzle has a vapor system, it can suck the fuel back into the station's system. BTDT. Happens particularly when you really try to max it and don't pull the nozzle out constantly to see what is going on.

2. Could have just been a miscalibrated gas pump too (as in, broken or fraud). Had that happen too--three gallons plus extra in a (non-Audi) tank I just flat out knew wasn't that big and had never taken a quantity of gas like that.

More generally, I am pretty skeptical of this line of reasoning. German companies are notorious stereotypically for their precision, and this theory cuts way the other way. Car companies also specifically want to boast about range, even more so with diesels probably, so why would they short the tank size in published specs? The range numbers are always estimated fuel economy times tank size. In things like advertised HP, they sometimes are accused of gaming it to try to hold the vehicle in a more economical insurance or registration fees class, and in displacement to hold it just under the true round number for similar registration or tax issues, but I've never heard of any such parameter affecting fuel tank size.

Last, notice on the Q5 Hybrid they cut the tank size a bit to fit the battery and auxiliaries stuff in. As a side note, a better result to me than the really dumb "just dump it in the trunk" hack job they did grafting the Q5 system into the A8 for a hybrid. Then true to the stereotype, they dutifully reported a much reduced trunk size that is already viewed as a negative on the D4 A8 vs. the prior D3 and the competitors in the class. That Q5 Hybrid tank spec is also published of course, side by side w/ the others. Once again, if I were an Audi marketer, it's not a stat I would actually prefer to come out that way.