calculated vs. computer MPG - Please post your results

With only 1,000 miles on my Prius V, my actual mileage was 2 mpg less that the computer's (52/54).

 

It appears from this thread that the 2010 Prius is over estimating the MPG readout on the dash display. This is a fact from my study with our car and the comments from 2010 Prius owners.

It would be beneficial if someone in this forum as a direct connection to Toyota that could advise them of this defect and perhaps have a soft ware fix to correct the problem.

I know for a fact that when the 2006 Honda Civic Hybrid was launched there was an error in the MPG display. That every 62 miles the MPG would reset and go back to zero. So after 61 miles you were getting a reading of 50 MPG when you went down a long grade after the 62 miles you would start to get a new current reading sometimes 90 MPG.

Honda recognized the problem and fixed it with a new instrument panel software or hardware, but they did fix it free of charge.

Alfon

 

I am getting 2-4 miles less (by my calculation) than what the car's readout indicates. I filled up yesterday with 419 miles on Trip A & took 9.1 gallons. That calculates to 46, compared to the 48.2 mpg displayed on my dashboard. This gap has been consistent over the 6 weeks & 3000 miles I've had the car.

 

I only recorded it for two tanks. They were:
Today, 17 Aug 09
318.3 miles driven per trip A
8.0926 Gal's pumped
39.296 mpg calculated
41.5 mpg from trip A display

13 Aug 09
356.4 miles driven per trip A
8.413 Gal's pumped
42.363 mpg calculated
44.3 mpg from trip A display

 

Thanks, GaBoater! Would you be able to keep this same information for several more tanks? Also, can you give the odometer reading (just so we know two things: 1. How new is the car; and 2. Whether there are any data gaps)?

 

I have filled up twice. Strangely, at my first fill-up, my calculated mpg, which had to be based on the dealer's tank of gas, was higher than my the trip display. On the second fill-up, it was 2 mpg lower, as reported by others.

7/31 Purchased car - dealer filled tank
8/8 6.98 gallons - Trip A display: 314 miles, 44.90 mpg; calculated: 45.01 mpg
8/18 8.26 gallons -Trip A display: 370 miles, 46.90 mpg; calculated: 44.79 mpg

 

HSI discrepencies for my recent EBH road trip:

545.6 miles 62.3MPG indicated 56.69 calculated 9.625 gal.

569.3 miles 56.6MPG indicated 50.97 calculated 11.17 gal.

476.2 miles 57.5MPG indicated 52.56 calculated 9.06 gal.

535.2 miles 59.9MPG indicated 54.61 calculated 9.80 gal.

598.2 miles 57.1MPG indicated 51.44 calculated 11.63 gal.

So we have differences of 9%, 10%, 8.5%, 9%, 10%. Doesn't help when your running long highway distances and have gas far between.

Wayne

 

Yes, but that bug did not affect all the 2006 models just a subset of the ones manufactured in the first few months... and the MICU software update/cluster update was available shortly afterward.

Also, that bug did not cause it to overestimate the aFE by the magnitude it does on my 2010 Prius. In fact, the pleasant and unique thing about the HCH-II that no other hybrid exhibits is that the displayed aFE is almost always (1-3) MPG lower than the calculated FE.

In any case, let's hope Toyota addresses this problem properly and without delay.

Cheers

 

Wayne,

It appears we have interestingly different approaches to measuring the differences between "indicated" and "calculated." My approach has been to state the percentage increase the indicated fuel economy is above the calculated fuel economy. Yours is to state the percentage that the calculated fuel economy is below the indicated fuel economy. The effect is that my percentages always will be higher than yours.

62.3MPG indicated 56.69 calculated; FireEng: 9.0% a priori: 9.9%

56.6MPG indicated 50.97 calculated; FireEng: 9.9% a priori: 11.0%

57.5MPG indicated 52.56 calculated; FireEng: 8.6% a priori: 9.4%

59.9MPG indicated 54.61 calculated; FireEng: 8.8% a priori: 9.7%

57.1MPG indicated 51.44 calculated; FireEng: 9.9% a priori: 11.0%

My indicated mileage is 5.0% higher than the calculated, but the calculated is 4.7% lower than the indicated.

I wonder why your differences are so much greater than mine?

 

I use less gas?? Maybe the 17 vs the 15 inch wheel combo and the known 3 MPG hit your taking. Add 3 mpg to your indicated and then see what happens.

Wayne

 

Thankfully, I don't have to take anything you say seriously!

Whatever difference exists between our tires, in terms of revolutions per mile, hardly seems to be enough to account for the more significant differences between indicated and calculated numbers for your car versus mine. Perhaps it is simply because your MPG numbers are just that much higher (your first reason!!).

 

I am on my second tank since getting mine this past Saturday.

odo 626 miles, (car had 304 miles on it when we bought it) so we put 326 miles on it.
Filled up with 6.11 gallons to give a 53.44 calculated average, and the car showed 54.3 average. So it is close enough for me.

 

One option is to break up your fill-up cycle to shorter intervals ... say twice a week:

• Friday evening - to measure weekly commuting usage
• Sunday evening - to measure weekend usage

After a month with eight fill-ups, there should be enough data to draw an inference about the error:

• Is it driving style related?
• Is it a fairly constant error for your vehicle?

Since my mph vs MPH and hill climb charts are based upon the vehicle generated display, checking the calibration is important. Fortunately, my wife suggested it was OK for me to start using her car on my daily commute. If she remains OK with this, I'll start the protocol this weekend and by the middle of September, I should have useful data for our ZVW30.

Bob Wilson

 

260.8 miles / indicated 57.7mpg/ calculated/ 55.31 mpg

214.7 miles / indicated 57.6 mpg / calculated / 56.47 mpg

alfon

 

New Prius owner here. We have about 2500 miles on our 2010 Prius IV. I see alot of you are posting 50+ MPG. I am only seeing 42-44 MPG on our display. I have not had the chance to figure it manually. Do these cars get better mileage as they get more miles on them? Most of the driving is city/rural. My best mileage was 48.5 and that was highway. Any tips on how 50+ MPG is achieved would be appreciated.

John

 

Miles MPG (DISP) MPG (CALC)
449.0 51.50 51.77
427.7 53.40 50.92
441.8 53.10 50.54
456.3 53.10 50.94

Typical commute is 45 miles round trip each day, 2/3 highway, 1/3 streets, no hills.

 

Guess my TAB key isn't working the way I expected...

 

I'm getting about the same or worse, due to this killer heat and humidity, and the fact almost all my driving is short trips. However, I have gotten over 51 on a trip to Galveston and back. Unfortunately, its even worse than it seems since the computer seems to be about 5% higher than actual measured mpg. You should do a bit better than me, since you have the 15 inch wheels.

 

Perhaps the software that Toyota used to figure out the mile per gallon was changed from the second gen Prius. I suggest this because with my 2008 Prius have something like the same issue but it's the opposite of what the 2010 seems to have. My Prius will say I did 45 miles per gallon but when I figure out this out manually, often about 5 to 7 miles per gallon off as to what I'm actually getting.

Steve

 

I think you were trying to make a table?

I'm using "|" as the column separator inside of the "[" "]" tag delimiters for "table" and "/table" text. Each row is just a single line.

Bob Wilson