MFD shows 49.6, calculation says 52.4

ystasino · Jun 18, 2007

<div class='quotetop'>QUOTE(workingfordogs @ Jun 17 2007, 12:27 PM) [snapback]463455[/snapback]</div>

Has Toyota told anyone how exactly they do their mpg calculations? Might explain the mpg discrepancies. What mileage number does the Prius calculation use? Could this also be an issue of individual cars being biased high or low on how the Prius does the mpg calculation?

My Prius calculated 55.4 mpg, and my hand calculations (odometer reading for the tank divided by gallons paid for) gave 53.1 mpg (about 4.3% error, the Prius is calculating that I used ~3 gal less gas than I paid for). This is over the course of 11 tanks of gas from March through June, filling up at different stations, with WI weights and measures certifying accuracy of the pumps, not overfilling (fill to first click), filling slowly, and pro-rating the Prius mpg calculations for the proportion of miles driven on that tank of gas. The odometer and fuel calculator are both reset at the same time when I restart the car after filling. The Prius underestimated the mpg 4x vs. overestimating it 7x. Biggest discrepancy was +10.7 mpg, lowest was +0.4 mpg

The salesman that I purchased the car from said that the Prius calculation was the right mpg because the fuel use is that measured at the #1 injector, and that the miles were prone to error ("just wheel rotations"). Ok, so, what number of miles other than the same odometer reading I'm using for calculations would the Prius be using?

Even if it was an issue of density of the gasoline as the weather warms up, the Prius should be calculating worse mileage on warmer fuel because the amount of energy in the same volume of fuel would be less (yes, that doesn't address what temperature the engine works better at).

More thoughts on this? Many thanks.
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Prius cars without the bladder (the source of variation of the capacity of the fuel tank as well as premature pump stops) apparently report decent accuracy as stated in the posts above. Set trip A to 0.0 drive for 4 tanks, write down how much you fill in after each trip and calculate a number of tanks and see how they average out.

MFD shows 49.6, calculation says 52.4

ystasino Active Member

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MFD shows 49.6, calculation says 52.4

ystasino Active Member