calculated vs. computer MPG - Please post your results

After 13,489 miles, I have seen an average of 6.33% error in the calculation of the indicated MPG compared with the actual MPG. Here are my actual results over the last ten months.

Actual Indicated Error
37.79 40.60 7.44%
44.28 46.50 5.02%
44.34 46.70 5.33%
47.48 50.70 6.78%
44.83 48.10 7.29%
46.21 48.60 5.17%
48.61 51.20 5.32%
46.40 50.20 8.18%
49.67 50.10 0.87% (this is probably an error, since it was a small fill up)
49.34 53.70 8.84%
48.89 51.70 5.75%
44.58 46.90 5.21%
44.77 48.10 7.43%
45.67 48.00 5.09%
47.56 50.90 7.02%
49.77 52.90 6.29%
48.07 51.00 6.10%
43.54 46.60 7.02%
40.65 43.80 7.74%
37.48 40.10 7.00%
37.02 40.00 8.06%
42.78 45.50 6.35%

 

Terrel, you are actually seeing the same exact error (mine is 6.43%) I see here on the other side of the planet...with the same swings in measurement.

 

act ind error
5.2 4.8 7.54%
5.3 4.9 7.58%

Not exactly a big sample, very new car, and just buckled down and started spreadsheet for the last 2 fill-ups. But very consistant error. The values are liters/100km.

This is with 195/65R15 snow tires on, in place of stock 215/45R17, the latter having outside diameter rougly 2% less. I don't think that would affect the error, since both the calc'd and indicated are dealing with the same odometer reading.

 

I am hearing that there is a bladder in the gas tank. Depending on the temperature, you may be able to get more or less gas in the tank. Does that have anything to do with it?

I have only filled up once and I have a 4mpg discrepancy.

Dave

 

No bladder after 2009 Prius model

 

The removal of the bladder for the 2010 model was one of the important selling points for me.

 

Good to know....THANKS!!!

 

but is this the prius or the fuelpomp error?
i did read something about fillup stations not reading the correct gallons
so thy read more to you pay more but ofcourse there is not getting more into the car

maybe take a reserve X gallons thing ( forget its name ) what you use when you get stranded done the road without fuel.
and see of X gallons are really X gallons

 

Sorry, posted in the wrong thread.

 

I have had similar results. After about 5 or 6 fill-ups, my MPG measuring from the pump runs about 2-3 miles per gallon lower than the reading on the dashboard. It's better than my 2004 Prius with its MPG, but still disappointing to see the difference.

 

My first real fill up today on my 2010 Prius IV with NAV (tank only had one bar left) and the computer said I had averaged 46.5 mpg and my manual calculation (miles driven/gallons) worked put to be 44.00 mpg. The car only has less the 700 miles on it, so it's far from the break-in period. My commute to work, if you want to call it that, is 3 miles on city streets with multiple stop lights. The ICE probably is warm enough to start "gliding" within 1.3 miles and I do glide when I can. Total commute time is around 7 minutes. Air pressure is what is on the placard on the driver's door. I live in San Diego and as a result our temps are pretty stable, except it has been in the upper 40's to low 50's in the AM and in the 60's-70's during the day. The AC is on occasionally. I have been keeping it in "regular" driving mode, so no ECO setting, since I'd like to experiment on the different settings. Initially I was a bit dissapointed with my results, but I realize I barely warm up the car and then I've arrived at work, plus all my other destinations are relatively close also, so the car doesn't get to run much more the 10-15 minutes before I have arrived to my final destination. One last comment, San Diego is peppered with hills and canyon, so the roads are constantly up and down, which I understand will hit my mpg's bottom line.

 

I have a 3rd generation Prius II which grossly overestimates my MPG. I have routinely calculated 4-5 mpg less than the computer-derived MPG. I asked the dealer service department if there is a way to adjust the computer/software/electronics to make this more accurate and the dealer informed me that there is no method to adjust the computer-derived MPG.

I realize that there is no way to calculate the MPG precisely. I would be happy with a 1-2 mpg difference, not 4-5 mpg difference.

 

Graywolf3458 - I understand your disappointment and I don't want to justify or protect Toyota - but at least there is one "positive" side to it - error is constant and doesn't change. And this is much better than always changing estimation. My error is consistently 6% on average. Since 23000km...
Obviously it would be better the FE calculation were a bit more accurate...

 

My 4th tank, first calculation:

@ 1227 miles

48.4 MPG (FCD)
45.8 MPG (Calc)

 

My 2010 Prius computer mileage is just about 5% higher than what I compute. Here are my results to date:

Date: Computer/ Calculated
9/24/10 48.3/45.9
10/7/10 48.5/46.0
10/29/10 49.1/45.5
11/2/10 47.5/44.7
11/13/10 48.2/45.5
11/30/10 44.3/41.6
12/14/10 40.4/38.1
12/26/10 40.5/38.5
1/13/11 38.5/35.8
2/11/11 38.8/35.7

I too am annoyed by all of the "Chicken Little" lights and beeping warnings about running out of gas when it thinks it's empty. Talk about the Nanny State. lol The most I have ever put in it so far is 9.96 gallons...and that was after a LOT of pestering. The tanks holds 11.9, so it has never been anywhere near empty. The miles to empty indicator is also out of whack when you get down to below an indicated quarter tank as well. It would be nice if these indicators could be more accurate. I'm surprised you can't punch in your actual fuel used somehow and have the computer correct itself.

But these are small concerns. The car is great on gas. Glad I got it...especially with the price of fuel lately!

 

50.2 MPG Indicated
46.8 calculated

I have noticed that during the winter months
the MPG is consistently off at least 3-4 MPG.

During summer months not as much.

I believe that weather is a factor in the difference
in calculated and indicated mpg.

alfon

 

Got my Prius less than 3 weeks ago but consumption so far as follows

1. 725 km - 39.5 lit = 18.5 km per lit. (reading 20km per lit)
2. 802 km - 39.2 lit = 20.5 km per lit. (reading 21.7km per lit)

Looks like 5-10% discrepancy

 

Over 9372km the trip computer gave an average of 5.0 L/100km. During this time I kept all fuel receipts and it calculated as 5.305 L/100km. That is a discrepency of 6.1%.
On my previous Golf (Rabbit) the error was 6.5%, but I could use the VAGCom to correct this. It's a pity no-one has worked out how to correct this on the Prius.

 

I did not get the information for my first tank, but here are the subsequent 4 tanks.

Miles___Gallons____MPG Calc____MPG Prius____Ratio
419____8.037______52.13________55.5________6.1%
465____9.209______50.49________54.3________7.0%
500____9.685______51.63________54.0________4.4%
531____9.892______53.68________56.8________5.5%

And, yeah, as best I can tell I could go another 150 miles from when the car start blinking at me to refill the tank and about 100 miles more when the car says I can go no more miles.

 

Hello everyone. I'm almost a newbie to the forum, although it helped me with a technical problem that my dealer could not solve. Anyway, wanted to place my input regarding mpg in our 2010 Gen III. Just completed a 3,500 mile trip to Florida and back to New England last week and I specifically recorded all our gas fill-ups compared to what the computer displayed. The spreadsheet I created stated that our lowest mpg during this trip was 46.4 mpg. Our highest was 52 mpg. The Toyota display always was about 6% higher than actual data calculated, just as some members have stated. But overall we were happy to average 49.8 mpg, mostly traveling interstates with the flow of traffic (65 to 75mph). Because I believe one can get better gas mileage with slightly higher tire pressures, we ran the psi at 37 on all 4 tires. Toyota recommends 35 psi front and 33 psi rear (at least on the tire information sticker). Wondering if the Prius computer is calculated for those exact tire pressures and if you over inflate it gives you a skewed reading? BTW our Prius turned over 30K during this trip.