Actual MPG vs. MFD reading Comparison Spreadsheet

[JimboK]

[DaveinOlyWA]

nice spreadsheet. pretty close to the same formula i use (i use open office btw, which is slightly better in features and MUCH better in price)

i also add additional calculations for winter and summer mileages since they are so different and cents per mile calculations.

also, on your 14 mpg difference. both the tank previous and after reflect a swing in the other direction. now you can blame the bladder if you want, but i would blame the pump you used.

now what i do is estimate the approximate amount of gas i need to replace what i have used. for example, if i drive 500 miles and got 50 mpg and i fill up and it stops at 9 gallons, i will dribble in up to at least 9.75 gallons since i know that there will be room for it. studies show that the auto shutoff on pumps malfunction up to 20% of the time anyway almost always shutting off too early

**edit**

ok, head was spinning over the volleyball match... forgot to add that

its all a comparison when tracking your mileage. there are many sources of errors that apply when doing all this, so basically the more data collected the better to evaluate your Pri's performance.

on my spreadsheet, i punch in the MFD reading for mpg and trip A for mileage to get my estimated gas usage which accounts for the MFD reading in signature. the estimated gas usage accounts for any LT stats.

on my 2004 with 30,000 miles difference was 1.9%
on my SPM difference is about 2.2 %
now on my 2010, had a major discrepancy on the last fillup which i may end of removing since i strongly suspect the pump ripped me off, but we shall see. will be doing another fillup probably within the next week or so. but no way it will make up a 1.3 gallon difference (actual fill 8.335 gallons, estimated fill 7.05 gallons)

just a side note. have to assume that this did not make a difference since i verified figures with the odometer. but during this tank is when i installed the door sills and like an idiot i followed instructions and disconnected the 12 volt battery which reset all the trip info. i did write down the info before doing this... so should not have made a difference, but anyway...

[gak27]

After almost a year of ownership and 26K+ miles, my lifetime MPG based on tank fill volumes is 47.4; the MFD lifetime is 48.8. I do essentially all of the calculations that others have mentioned above (calculated MFD gallons, MPG per tank, etc.). My cumulative gallons used based on fill volumes is 554.6 gallons, 538.9 gallons based on MFD MPGs. This gives me an lifetime average error of 2.8% or around 0.24 gallons/fillup. I do my lifetime calculations as running tallies, not averages of individual tanks...I have by tank, month, and season plots set up for lifetime and tank values...