Calculated MPG

Matt wrote:
Most fuel gauges are nearly useless even the ones that I carefully calibrated, the tank shapes just make it that way.

Grit dog wrote:
Interesting statement….
Maybe applies to antique vehicles?

Grit, I am guessing that you mean as opposed to the modern systems that tell you "Miles to Empty"?

toedtoes wrote:
Years ago, I took my young nieces "up the hill" to the snow. We had a great day. When it was time to go home, the computer read that I had about 20 miles til empty. I made a big deal about that to the girls and then said "oh, let's take a risk" and started down the hill without filling up. Over the next 60 miles, every time we'd pass a gas station they'd beg me to stop and fill up. I wouldn't. After we had gotten all the way down, I finally stopped and they practically cheered in relief.

Well Grit, the practical matter is that the body computer reads the fuel level off the same old "float and resistor" sender that has been in use since cars started having electrical systems. It uses that to record a fill up (if less that a fill, it fakes it), then it uses the injector pulse width to total up the fuel used. If every thing is good, this can be pretty close. (I did own a VW that had a mechanical gauge, and I got the reserve valve from an older model because I still couldn't trust it.) So, if you live out side of New Jersey and can fill your own tank, you can create some repeatability there, but the instruments are still problematic. If you could see the efforts that have been put into both road vehicle and aircraft fuel quantity measurements, you would be surprised by the range of technology uses in these efforts and the total lack of success.
I always fall back on the line in a FAA manual that says that the only time you should believe what a fuel gauge says is when it says "Empty".

Matt- a refugee from the labs of Detroit