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Discussion Starter · #1 ·
I just filled up my first tank on the Prius and I manualy caculated the Fuel Economy. My traveling has been both Highway and City. Temp outside has been arround 40 here in New England. I had to do the math several times and I came up with the same 58.50 MPG !!! I still cant belive it !! I guess driving like Joe Friday in the Movie "Dragnet" pays off.

Cheap Bob !!!!!!

May with all the fuel savings I wont have to be cheap anymore!
 

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You can't go by the calculated MPG on just one tank, because you can't be certain that you filled the tank exactly to the level you started. This is especially true on account of the bladder.

So, if your calculated is significantly higher than the display, your next tank may be significantly less as you compensate for the short tank.

However, over several tanks, say 5, the error disperses out over the average fillup size.
 

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Well, I reset the trip counter when I fill up the tank, and check number of miles I ran when I am filling up my next time and divide that by number of gallons it takes to fill my tank up again.

I am not sure what makes it so complex to calculate miles per gallon!
 

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Sakhiya said:
Well, I reset the trip counter when I fill up the tank, and check number of miles I ran when I am filling up my next time and divide that by number of gallons it takes to fill my tank up again.

I am not sure what makes it so complex to calculate miles per gallon!
The calculation is easy, of course. It's just that the Prius has an expandable bladder in the gas tank that will vary in how much gas it will allow you to put in from fill to fill. Temperature will affect it quite a bit. So if the first tank-full had one gallon more than you were able to put in on the refill, it will make a BIG differance in your calculated mpg. For any single tank-full the indicated mpg on the screen will be more reliable. Over many tank fills, the bladder varience will average out and you will get good (perhaps better if you believe the pump calibration) numbers.
 

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Putting it another way: you don't know how much was left in the tank when you started filling it, and you don't know how full the bladder gets on this fillup. Therefore the amount in this fillup is usually not the same as the amount you burned since the last fillup.

Trust the displayed MPG. It is more accurate than manual calculation because it uses the amount of gas sprayed by each actuation of the fuel !njectors, which is calibrated to an error less than 3%.
 

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Discussion Starter · #6 ·
Thank you all! Its still great even if its off a little bit. Either way its still a great car!
 
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