calculated vs. computer MPG - Please post your results

Toyota knows that there is a problem with the mpg computer always over reading even with the 2015 Prius and Toyota has known this for years at least since the 2010 Prius model year. Toyota should correct this in accuracy with the 2016 Prius as the engineers and people at Toyota in charge would have to be complete idiots not too...

 

true...but, it's the in·complete idiots that I worry about.

 

FWIW, even when my ScanGauge shows fan speed 4 (outa 6 I think), I still can't hear it. My ears are getting on, and a bit shot tho.

 

Hmm ... Not even with engine, HVAC fan, radio, and any other noisy components off, and no significant outside or copilot noise? I'd assumed, perhaps wrongly, that the battery fan would be fairly obvious in its upper speeds.

 

The time I recall seeing fan speed 4 was in congested traffic. Couldn't hear it. But yeah, I'm thinking when you can hear it, must be full speed. Which is 6 I believe.

 

I have 35,000 miles under my belt since last July and I've refueled 102 times, shutting off on the first click every time with the exception of twice when I only added a 2-3 gallons and left. I didn't fill it up because I wasn't happy with the stations, the pumps kept shutting off. Anyway, my manually computed mileage has been anywhere from 3% higher to 9.9% lower than the CONS display, so I don't know how they'd correct that. I know some folks say it's always off by 5%, but that hasn't been my experience. The one thing that has been fairly consistent is the times I've run until the fuel gauge started blinking, it's always taken between 9.5 and 9.9 gallons depending on how close to or past 0 I drove. While I enjoy tracking my mileage, all I really care about is how accurate the fuel gauge is.

 

Our 2014 Prius-4 isn't always 5% off, sometimes it's 6% or 7% off, but it's NEVER been less than 5% error. And, I, too, religiously adhere to the "one-click" at same pump rule.

 

Pumping method cannot create, and sustain, an error in mpg. If you do manage to introduce an error, due to filling a little more or less than usual, the error will cancel out at the next fill up. The more fillups, the more accurate the overall calculation becomes.

 

However, repeated errors (making same mistake over & over) quite often manifest as an "additive" error.

 

True, if the person competently keeps track of a long-term average. In some cases, that's a big "IF."

 

I suppose the fact that most of my fill-ups are all over the country might have something to do with my experience.

 

The errors due to fill up are inherently self-correcting. One time the pump shut's off a little sooner, with the next fillup you recoup it. My error zigs and zags, but closing in on 5 years of calculation now, the mean is 7.45%. Pretty much impossible to budge.

 

The MEAN (µ) and STANDARD DEVIATION (σ) numbers would "tell" the tale...numerically.

 

I kind of get that, but my comment was related more to how should Toyota correct the CONS display given those variances on each fill-up. If they lower it by 7.5%, you still get differences, just different ones, so what's the point? And your mean might be different than others. My overall mean right now is 5.3%, but it varies from 4.9% to 6.4% for the 4 trips we've been on (with 17, 21, 23 and 28 fill-ups for those trips - out of 102 total). I have to admit that the display on my '99 Montana van was pretty accurate, but there was no hybrid battery power involved. I guess we'll have to see if the CONS display is more accurate on the Gen IV.

 

I have been stumped that the gauge reads almost empty, but my mental calculations say I should have about another 80 miles to drive. I just thought it was a gauge error but now see it is a common issue. This is my second prius (2015), the first (2006) was very accurate with the gauge.
I have always only managed about 45 mpg on either car.

 

IIRC, Toyota has the gauge read empty before you get there to avoid idiots running out of gas (which is a complex fix on a Prius compared to standard cars).

 

Wouldn't the state of charge in the battery during the first fill up and the state of charge on the next have a big influence ?

 

Not when gasoline is what's being consumed and measured.

 

For my 217 fill ups, the mean difference between displayed mileage and calculated mileage is 0.057 (5.7%) and the standard deviation is 0.011883 (1.2%). Maximum = 9.5%. Minimum = 0.8%.

 

2012 Five. 17" tires.
I've only had it for about two months and I've driven under 2500 miles.

Last tank:
400 miles
57.0 mpg displayed
54.1 mpg calculated