Mathematically speaking, the fuel efficiency calculation (amount of fuel added and distance covered from previous tank) has a missing constant. That constant is the maximum fuel level, which for pragmatism is left as an unknown. This maximum fuel level becomes an implied factor over several tank fills; Whatever discrepancy there is between one refill and the maximum fuel level gets covered by the successive refills (it is not compounded, the difference is only on the latest tank). This is why calculating single tank fuel efficiency is inherently inaccurate, whereas getting the average over several tanks is reasonably accurate.

Example: If you super-fill one tank, say as a one-off experiment, then that tank's fuel efficiency will be relatively poor.

Example: If you under-fill one tank, then that tank's fuel efficiency will be relatively better.

(Both examples create an exaggeration to the fuel efficiency of the previous trip)

Going from gas station to gas station, pump to pump, there will usually be some deviation or inconsistency in just how full your tank becomes. The different nozzles may click off with different tolerances. But this doesn't matter when you take all of the above in mind about averages. This is why I take the tact that there is no point to being **** about having the exact same fuel level whenever leaving the gas station or giving individual tank fuel efficiency much weight; The degree of error gets eliminated by looking at more than one tank and there is a lot less anxiety involved.

 

My last tank went 652.4 miles, and the last 92.7 miles of that were after the low fuel light went on. Total gas at fillup was 11.929 gallons, with the click coming on at just over 11 gallons. The previous fillup was stopped at the first click (it was $43.00, and an even dollar amount was too odd to pass up), so the MPG of 54.7 was somewhat reduced. Nevertheless, I'm pretty confident that 100 miles after the fuel light comes on is not out of the question. I've routinely gone 70-80 miles with no problems.

 

Last night I hit my first 600 mile tank. I filled up to the first click with 10.5 gallons, meaning I still had almost another 100 miles in the tank. As so as I get my FE up a little higher, I think 700 miles is attainable. Just have to get used to the idea of driving around for a couple of days with no bars on the fuel guage.


The most fun you can have while driving so slow!

 

Yep, a 700mi tank is (somewhat) easily doable

 

Agreed. I've got a few 700s, one 800, one 900, and one 1,000 mile tank. Some of those were a little bit more work.