gas mileage

"Search" is your friend and will help you

 

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

 

My car used to say it was getting 35mpg on the MFD. In fact I was putting in much less gas than that. The amount of gas I was putting in was like 45 to 48mpg. I replaced all 4 injectors because they were clogged. And now my display reads 48mpg. Over 300,000 miles on my gen 1 Prius.