computer mileage

Because of the Prius' flexible fuel bladder, comparisons based on a single tank can be unreliable. Instead, base your comparisons on several tanks. Some of us have tracked the differences for an extended period (about 7 months for me, many years for others). Most report the display to be about 2-4% higher than calculated.

 

For what it's worth- I drove my Pri 7808 miles in the first year, burning 172.2 gallons of gas. That averages out to 45.3 MPG, which is close to the average of the computer indicated MPG of 45.5 MPG.
I agree with "jimboK" you should take a reading over a somewhat long period of time, due to all the variables effecting the MPG, i.e., tank bladder, temperatures, fuel pump accuracy, etc.

 

A statistical analysis can't tell you a thing -- you just don't have enough reliable information upon which you can base any analytical determination.

The bladder in the gas tank means your tank-by-tank MPG calculations are unreliable. I have had a tank where the calculated MPG was 73.065 but the MFD reading was 51.0 mpg. I've also had a calculated MPG of 36.104 for one tank where the MFD showed 50.2 mpg (for the same tank). The most telling thing: These two tanks were back-to-back.

Across 10,000 miles, the MFD reading appears to be nearly 3% higher than my calculated MPG. The MFD is 49.9, while the calculated MPGs are 48.5. One reason for the difference is that I am not certain exactly how full the tank was when I received the car from my dealer. I expect the difference betwee MFD and calculated MPG to narrow further over time.

 

Nope. In my experience there is no correlation. Here are the calculated/MFD figures for my tanks this year.

49.0/51.6
49.3/51.5
59.8/54.9
47.1/58.0
54.0/54.1
58.0/55.3
54.1/56.6
54.7/59.8
57.9/61.4

Lifetime is 51.5 calculated over 23895 miles up from 51.1 over 20538 on 1/2/08.

 

From reading various threads here (search for "guess gauge" and "bladder"), it seems that 2004-2005 models had an MFD MPG that was about 3-4% optimistic, while the more recent cars were only 1-2% optimistic. I was surprised to see someone on this thread with a 2007 that was 3% optimistic, though.

My own history (for my 2005) shows weighted MFD MPG of 47.8, while my calculated MPG is 46.3. See the last line of this table:
Gas Tank History

 

Taking one variable out of the equation, my Prius does not have the dreaded bladder, just plain old plastic tank, or whatever.

I filled up tonight and MFD indicated was 46.0 mpg on the tank full. After fill up, calculated from full tank to full tank was 46.1 mpg. Poor economy, yes, I'm working on it, but in terms of accuracy, I'm very happy with the MFD read-out. The previous tank-to-tank fill up was only out 0.2 mpg too at 45.8 mpg.

Hope that assists. Any other non-bladder Prius' with similar accuracy ?

 

???

how did u come up with that estimation

 

My actual mileage nearly always comes out WORSE than the computer display. Interesting to learn that this is the opposite of what most others are getting. I guess my "conspiracy theory" about is wrong.

 

I'm only about 1100 miles into my new '08 Prius...the difference between display and calculation of the first tank was nil. The second tank calculated at 37.9 but displayed at 42.3. I would assume by reading this thread that I should not be concerned, and that it should be fairly accurate over time...correct?

 

That is correct. Mine have been off by as much as 15%+. For reference, here are my figures tracked for almost a year:



FYI, the "Weighted Diff." column adjusts for miles driven with each tank, with the numbers in that column averaged for the last column.

 

I have a 2007 with 20700 miles on it. I've been keeping track of all fill-ups and have a difference of about 5.4% with the MFD reading high. MFD based total mileage is 49.2, and calculated from actual fill-ups is 46.7.

I am wondering if there is an adjustment that can be made to "tune" the MFD reading. This seems to be a relatively significant error.