MPG Readout

There's several threads here on this topic. Most of us accept that the reported mpg is optimistic by a few points.

SCH-I535

 

Here's some of the threads:

https://www.google.com/url?sa=t&source=web&rct=j&ei=gjuRU-ThGM_goASomYKwDA&url=http://priuschat.com/threads/which-mpg-is-right.141648/&cd=6&ved=0CCwQFjAF&usg=AFQjCNGk2UQXNcRfAFlPi6GCLesTuniggw

https://www.google.com/url?sa=t&source=web&rct=j&ei=gjuRU-ThGM_goASomYKwDA&url=http://priuschat.com/threads/accurate-mpg-display.25900/&cd=10&ved=0CDkQFjAJ&usg=AFQjCNEWvOweFPq7seFEoFQizxThxe3C3g

https://www.google.com/url?sa=t&source=web&rct=j&ei=5DuRU6zgNNTYoATDm4C4CA&url=http://priuschat.com/threads/calculated-vs-computer-mpg-please-post-your-results.65053/&cd=18&ved=0CDcQFjAHOAo&usg=AFQjCNEi8wHxSgikaul-H4Yj19QY-WmY6w

SCH-I535

 

I've found this to be true in other cars as well, it's not unique to the Prius.

 

i think it's because the speedo is faster than your actual speed so you won't speed.

 

Nope. The MPG is based on the odo, not the speedo. Odometers are not biased high, at these not anymore.

 

Doesn't excuse it. And it's by no means impossible to have a reasonably accurate mpg display: our second gen Civic Hybrid's mpg display was either spot-on or very slightly pessimistic. The only reason I can see for consistent, gross exaggeration reporting of fuel economy is..., well what do you think?

 

The EPA estimates are just that. Manufactures are required to report these estimates within a certain accuracy. There are, of coarse, upper and lower fudge factors that the EPA has to allow. Bear in mind the the reported fuel mileage figures that are published are huge for marketing strategies. So, if you are in the business of selling cars, wouldn't you take every advantage available to make your products shine in a brighter light ? Yes, indeed!

 

The OP is talking about the calculated mpg on the MFD vs. calculated mpg, not the EPA mpg estimates.

 

The PRIUS Engine Control Module (ECM) uses an abacus instead of a computer to do it's "calculations" maybe? (wink,wink)

 

But why computer always estimates 2-3 mpg more but not less? I would love to see 47 on computer but 50 with manual calculation?

 

Based on the many threads on this subject, the onboard MPG readout tends to be about 5% optimistic. As to the 'why" I have no idea, but I can't imagine it's a mistake or error given how consistent it is across cars. It's certainly to Toyota's benefit to have that onboard be optimistic since the vast majority of drivers trust it and don't bother to hand-calculate tank after tank to get a proper number.

(Edited my typo, 5%, not 2%, is what I've observed as well)

 

My dash-vs-calculated error is currently at 7.64%. That's with close to 43000 km's calculated.

 

When I traded it in, my 2010's error was similar -- 6.63% over 36k miles.
I'm way behind on entering my 2012's fuel log into the spreadsheet, so don't have its current figure.

 

So far (only 2,000 miles), our 2014 Prius·4 has consistently been 5% optimistic at each & every tank fillup.

 

I assume that none of us are really that upset. In the end, it's still a very nice number. So I have to ask...

 

Corrected my error, I meant to type 5%.

 

It's doesn't actually "matter" but what's the harm in discussing it?

 

...and, what HARM would it cause *IF* Toyota simply "corrected" the algorithm to provide an ACCURATE value?

 

None at all. That's why we're all here.