mpg inconsistencies

[InitialCivic]

Story time so I drove home and back around 8 hours and of course tracked the mpg. according to the scangauge e (which has been fairly accurate thus far) I got 44.5mpg driving home, then got 45.1 on the drive back until i ran out. This seemed to be about right with all the slow driving and occasional drafting. However on the fill up the mpg was only at 40.2 total for the tank. 444.5 miles put in 11.1 gal.

Seemed far too low for all highway so I kept going, on the last hour of the drive I drove a bit more spirited/ sped more and averaged 36.9 (according to the gauge) fair enough. But upon filling up it said my avg was 41.2 which has me baffled. 55.2 miles then putting back in 1.34 until it clicked.

Anyone have any similar experiences or can explain it because I am confused to no end haha. The first run I got some cheap gas so was thinking perhaps that could've caused the mpg to be lower than normal but that doesnt explain why the last fill up it was higher.

[mpg_numbers_guy]

Probably due to inconsistencies when filling up. Fill up only to the first click and get gas at the same gas station and pump if possible.

Gas stations are given a slight allowance so one station may have been more generous.

Also, the margin of error is quite large when filling up after such a short distance. Compare whole tank averages to get better data.

[slowmover]

Tank by tank doesn’t mean anything. It’s the average over time. A full calendar year, in essence.

Use records.

AVERAGE MPG and AVERAGE MPH will get you places.

Cutting unnecessary trips (cold starts), combining the rest reduces annual miles. This discipline pays biggest dividends.

Second is driving remaining miles at a higher skill level. Every trip has a plan (no left turns, best warm-up, etc).

Trying to find best possible MPG on a closed loop worth the effort, IMO. Involves first running 45-50 miles or more to get everything (including tires) warmed up. THEN fill tank to first auto shutoff. Run the (preferably) 100-mile loop back to that same fuel station pump in as close to steady-state as possible. Cruise control for low variation.

The competition is against one’s self. Absolute numbers don’t matter. It’s the percentage change from the original number set.

20% would be quite good.

Lower total annual miles & higher average MPH will combine to reduce the per-mile cost of fuel better than any other approach. While accomplishing same ends.

[roosterk0031]

1.34 gallon is too small of fill to get a good number. I like to track my 3-tank that way it averages out some of the filling inconsistency and go at least below half tank before refilling.