Did I really just get 57mpg in my 2009 Prius?

I am confused if you have a 2009 or 2010 Prius. Your profile says 2010. Makes a big difference.

Anyhow you did the math right 340/6, but there is variability in the pumps etc. Another gasoline pump you might have got 7 gals gaso and that would be 49 MPG or even 8 and that would be 42 MPG. So you have to do the math for each time fill-up and take some averages.

I usually keep the receipt and hand-enter miles on top of it. Then I enter miles, gallons, and cost for every fill-up and do some averages.

 

In North America, the gen 2 Prius has a flexible bladder inside the metal tank. This bladder has a random volume based somewhat on the outside temperature at the instant you fill up. I could get 11 gallons in 100+ F summer heat with 90% humidity with my Gen 2, but folks in Minnesota in the winter report 6 gallons. To add to the randomness, it folds differently at different times, making the Pips appear to be different sized.

I would enter your fillups into fuelly.com and let it average your mileage over time.

If the last pip ever blinks, get gas NOW!

 

I hope you figure out if it is a 2010 (gen 3) or 2009 (gen 2) as almost every piece of advice you get will differ between them.

 

No the pumps are tested and are quite accurate as far as I know. The fuel tank system and pump system work together and decide when you are full, but there is variability in amount of fullness, and if you really have a 2009 Gen2, you have the so-called "guess tank" flexible tank.

 

Basically yes...sometimes my tank gets really full, and you can tell because you get 100-150 miles before the first "pip" goes out. Warm days the tank takes in more.

 

Something else to remember is that the Prius is just like all other car's - it gets its best mileage during the summer. During the winter it is normal for the MPG to be lower.

I would suggest you sign up at fuelly.com and start recording your fuel usage there. If you do that, you will have a better understanding of what your actual mileage is.

On your car, per tank calculations are pretty much useless due to the bladder. To get a true average you need to average several tanks together.

If you want information on which package you really have, read the attached file. It has a section which covers what package comes with what on your '09.

Please update your avatar with your location also. It helps other's when answering questions on post's you make.

 

Getting 57MPG in a GenII isn't out of the question, but its probably not going to happen if you're not trying to get such good numbers.
As everyone else has said, going off one tank can be very misleading because of the bladder. The MFD is a much better way to figure out your mileage for a single tank. Most people find the MFD to be about 2MPG high, but pretty consistent.

 

Its possible with summer gas and all the ambient heat. But, if you join Fuelly like a lot of us have you can track your mileage more closely. If you have a high like you had, I will bet the next tank will be the low. Just average the two, no worries, it will all even out in the end. I got 65.9 MPG for a high followed by a 41.3 MPG. Before that high number I got 41.1 MPG.