i3adSaab

hey guys....since I got this car back around April I've noticed that when I fill the tank up its taking alot less fuel than the gauge would indicate it should need.

I just filled up today and actually did the calculation, been meaning to do this for a month or so but oh well....here're the numbers:

Tank capacity is 16.3 gal (U.S. TT w/3.2 quattro)
My gauge was halfway between 1/4 and the top of the red warning, so I calculate this to be approximately the level with 3.06 gal remaining.
So, the tank should require 13.2 gal to fill it up.
I filled it, and it only took 11.3 gallons.

Ok, I know this isn't an exact science but I've never noticed it with other cars, and this is a 12% error. I only fill the tank until the pump turns off automatically, never top it off. So, if I took 11.3 gallons that says my tank had 30.7% fuel remaining. But, I was far under the 1/4 tank mark on the gauge.

Well, you'd think I'd have better things to do with my life, but this has been bugging me. Has anyone else noticed this?

tnanks ahead.....Jim

Jason S

To verify the 16.8 gal, you will either have to pull the tank and perform a calibrated fill to figure out how large the tank actually is, or you could just run the car until it runs out of gas and then see how much fuel it actually takes. TBH I dont put much faith in the accuracy of the flow meters at the fuel pumps anyways and I do my best to try and not think about how inaccurate they might actually be. Admittedly, the stations I frequent give relatively consistent numbers when I fill up.

I see similar results when ever I put fuel in my '08 3.2. If I take it down to the first part of the red it will take about 12-13 gal. to fill it. I've had the fuel light on before and only put in 14 gal. The computer said I had 10 miles worth of fuel left, but it only indicates in increments of 5 miles.

It could be that the actual volume of the tank is 16.8 gal. leaving us with a useable capacity of about 15 or so. Or, it could be that these gages, having never been properly calibrated, just aren't that accurate.

I can say that when I fill my tank, the computer says my range is about 260-280 miles. I usually wait until I have 225 +/- 25 mile before I will stop for gas, and then the car usually takes 10-12 gal. If I remember correctly my average, as calculated by the computer, is 20.1 mpg.

i3adSaab

yea it just seems odd. Never noticed this on my A4. I fill at various gas stations with similar results, so I'm pretty sure the problem lies with the TT gauge....

i3adSaab

sorry, wanted to bump this message to the top....anyone else noticed this issue?

TTRob

I filled mine up yesterday. The gas light just came on as I was pulling in to the station. It said I had 35 miles till empty. Topped it off with 12.27 gal. Could the specs be wrong? The 2.0 only has a 14.5 gal tank.

Cabern A

I think that part of the issue is that analog gauges are not that accurate to begin with. They are not typically "linear" in their deflection, so if it is accurate at full, empty and half full - that's about all you can ask. Typically the smaller the gauge is, the more inaccurate it is.

Another part could be the actual fuel sender in the tank itself, since it is (the tank)a fairly unique shape, not rectangular, it will drain at a non-linear rate. This will make the sender inaccurate, to a degree.

All these things tend to make them inaccurate. The best you can do is know the car and fuel gauge itself and adapt.

TTRob

Filled up again today. Fuel light came on yesterday, 12.6 gal. I don't usually wait for the light to come on, just happened to do so the last two times I have filled up.

i3adSaab

I filled up Sunday after gas light came on also. I drove about 10 miles after the light first came on, then filled up with I think 12.7 gallons, can't remember exact amount.....but, with over 16 gallon tank, seems either the light is coming on early or the tank is smaller than the spec, as you mentioned above.

Can anyone else confirm, are we sure the tank is over 16 gallons?

i3adSaab

sorry to bump this up again....

fuel light came on today, which the book says will come on with 1.9 gal remaining. I drove about 6 miles then filled up, it took 12.7 gal.

It should have taken at least 14.5 gal, man this is really annoying. If the tank is smaller than specified, that's ok,....but it seems I'm filling up more often than I need to. My gauge moves to 1/4 full really quickly.

The only way to verify the exact tank size is to run it dry sometime.