Regarding the subject of MPG, on my 1st-2-weeks-of-July loop from NV through ID, UT and MT, I decided that one of the things I really wanted to know was how much fuel I had at a given gauge reading. This is something I don't see anybody do with their off-road machines, but I'm pretty paranoid about running out of gas but also like to get far from gas stations, so I'm meticulous about keeping current fuel-use records. It provides a pretty good comfort margin to know how much fuel you really have based on the gauge reading.
So I built a sheet to prompt me to record gauge position as part of my fuel records. I also figured I might want to gather statistics on mileage under various conditions, using different octane fuels, etc, so I added an octane column and add notes regarding driving conditions.
For anybody that might find it useful, it's attached here as a pdf. The idea is that you fold it in half so it stores more conveniently in the cockpit. That's why there are headings mid-page as well as at the top.
I tried to attach it as an Excel file also but apparently that's not allowed. I fill mine in by hand in the truck and transcribe the numbers into the spreadsheet later. The MPG column does its own math of course, as do the average $/gal and average MPG cells at the top.
And FWIW I averaged 12.3 MPG on that trip.
Here are some gauge indication and fuel-needed correlations from my rig, a gasoline-powered 2008 E-350 with what I am pretty sure is a 35-gallon tank based on the cryptic entry in the owner's manual:
Gauge says Fuel needed
3/4 tank 6.5g
1/2 tank 13.4g
on red line of E 27.8g
For whatever reason I have not yet managed to buy fuel when I'm on 1/4 tank.
If I really have a 35 gallon tank, it means I have 7 actual gallons left in the tank when it's on the red "reserve" line. Then there's the difficult-and-possibly-undesirable-to-answer question regarding how much of that fuel is usable. Maybe there are 7 gallons left and maybe only 2 of it is usable. Who knows? I don't find anything published on the subject. And running the thing out of gas (which I will choose not to do, of course) seems like the only real way to answer the question.
If anybody has good information on usable-fuel, please share it.