calculated vs. computer MPG - Please post your results

[F8L]

I am insterested in seeing how many people are experiencing wide swings in hand calculated MPG vs. computer derived MPG (FCD).

I see a lot of high numbers from many new owners but it seems the ones who are tracking MPG with both methods are seeing wide swings of 6-10MPG less than the computer MPG. I would like to see if this is a common issue and the car is overestimating the MPG or if maybe there is an issue specific to say Dave's car or his fill-up stations.

We have established through robust recordkeeping that the GenII is within 1%-3% or so from the MFD but I would like to see the same kind of data for the GenIII but since I cannot do it myself I am asking for you GenIII folks to perform the task. At least over a few tanks.

Please post your MPG offset* (FCD MPG vs. hand calculated MPG) AND the month your Prius was manufactured**.

* Offset is the difference between your FCD MPG and your hand calculations (divide miles driven by # of gallons pumped) Please ensure you have done this over as many tanks as possible. A few of tanks is not enough data.

** Manufacture date can be found inside the drivers side door jamb

[a priori]

I had thought I would wait until I had more tank fills to talk about this, but I'll try to put together a decent analysis of it and post it here.

The short of it is that I am seeing some differences not unlike what I saw in my Gen2. My first fill up was dead on with the MID display, but I think that the later fills only showed that what I got from the dealer was something less than a full tank of gas.

[F8L]

That would be great. I look forward to seeing your results. With people like you reporting we don't have to worry about the accuracy of the information. Thanks!

[alfon]

2010 Toyota Prius III with Navi

With close to 5,000 miles I have noticed the MPG guage is off usually 2-3 MPG in the positive.

My last tank was calculated by miles driven and gallons used at 54.6 MPG the guage read exactly 57.0 MPG.

Alfon

[fuzzy1]

I probably shouldn't chime in just yet, with only N=1 (57.1 displayed / 55.4 computed). The next month should push my N up to at least 5.

[cantgoback]

This may be an old question but for newbies like myself, does anyone know why the MID MPG is higher than what someone computes from the miles and gallons? Is there some rounding error in the calculations? Or is there an error in the gas level gauge? Or something else??

[HTMLSpinnr]

F8L - here's what my tracking charts look like thus far - the gap gets wider as display MPG gets higher.

[FireEngineer]

Originally Posted by HTMLSpinnr

F8L - here's what my tracking charts look like thus far - the gap gets wider as display MPG gets higher.

Exact same thing I'm seeing Rick. As the MPG heads north of 60 MPG the gap gets wider between actual and HSI MPG. Somethings not right here, my Gen II did not have a wide discrepency on my mid 70's tanks.

Wayne

[F8L]

Thank you guys for posting up. I think if we gather enough data that shows there may be a large discrepancy between the MID and the calculated MPG then we can persuade Toyota to pay more attention to this issue on future models or maybe make changes to the software currently handling the calculations. That is if there is indeed a problem.

[eldiee]

On our 2010 V we show 54.0 for 1010 miles. Fuel used 19.5 gal. or about 52mpg. I guess it is a little bit high on the car read out. So far we have been really happy with the mpg.