Would anyone have a logical explanation as to why there is a 4 to 5 mpg difference between the indicated mpg on the instrument panel and the calculated mpg based on miles driven vs. gallons at fill up on my new 2010 Prius? Don't get me wrong, I love the car. I just wished the indicated mpg were more reliable. Wes T.
How many times have you filled? How many tanks of gas are you totaling for your calculation? The short answer is that there is some discrepancy between displayed and actual mileage. A bigger factor is usually the variation of full when filling your tank. This introduces short term inconsistencies in your mileage calculations. If you total several tanks the variation should cancel out. Tom
Yup, if you know what to search on. http://priuschat.com/forums/gen-iii...y/66149-2010-toyota-prius-fcd-inaccuracy.html http://priuschat.com/forums/gen-iii...838-thoughts-mpg-variance-data-gathering.html http://priuschat.com/forums/gen-iii...vs-computer-mpg-please-post-your-results.html
I didn't search or read, buy I think it's as simple as this. Displayed mileage is calculated fuel flow. I bet there is no actual fuel flow measuring device
Another hypothesis. The fuel flow was based on pure gasoline and fuel containing ethanol has a lower specific gravity and is "thinner". In other words with the only variable being fuel, there is actually more fuel that flows through the injector with fuel containing ethanol than pure gasoline.
Fuel flow is calculated by timing the injector pulses, which is how the engine ECU controls the fuel/air ratio. As a result, the volume measurement is very precise, but also each volume is very small. Small round-off errors accumulate over time, producing a slight but consistent error. Tom
