calculated vs. computer MPG - Please post your results

Computer is usually about 5% higher than calculated MPG. I found this consistent with my fillups.

 

My lowest variance has been 5%, highest has been 9%, average this winter has been 7% just about...

Maybe the variance is higher in the winter?

My last few tanks have been in the 39's for mpg. And that's driving the speed limit... Can't seem to break 400 miles per tank either but it is cold as all heck around here... And I have the 17" handicap..

 

^ 7% sounds about right. I have the 17" too, from time to time wonder if Toyota adjusted the odo for the slightly smaller diameter, guessing not. I've tracked 48,000 km's this what I'm getting:

 

I've got over 10 years of data across a 2004 and 2007 Prius. My bias shows 1.4 mpg delta between the car computer display and the fill calculation. http://www.enerjazz.com/prius

 

Try plotting your MID(dashboard) mpg versus your PUMP mpg and see how close/far their coincident "line" is from 45º degree angle.

 

10 Tanks between 4.2 (first tank we can throw than one out .. ) 5.6 MPG low computed vs car. and so last 9 tanks between 5.2% and 5.6% low or about 2.6-2.8 MPG error. So 1 of 3 things. THey car doesn't actually computer the proper amount of distance, the card doesn't understand the amount of fuel it uses, they are lying to make folks feel better and can get away with it because it kinda matches the "official" EPA ratings.

 

^ I'd vote for the last option.

Today we started out with a virtually reset Trip A, only about 2 km from the gas station to home. Anyway, drove about 30 kms, with both Scangauge and the trip meter displaying liters per 100 km. They started out neck-and-neck, but pretty soon the dash display dropped to 0.1 lower, then 0.2 lower. Typical tank, calculated vs displayed will vary by 0.3. Say 4.8 calculated vs 4.5 displayed. 7% on average.

 

My mpg with my 2013 prius c is always less than 2 mpg off itf calculating from pump and odometer reading. I use the whole tank down past the 0 mile to empty and get gas at the same station. Could cars set to kilometer per liter or other settings that the computer makes more errors. I dont like that the error is always overstaiting the mpg.

 

First fill up. Gauge: 56.7mpg. Actual: 53.2

Albeit, I was driving it to get a feel for the car (I enjoy Power mode quite a bit), this was mostly long distance driving. Aka: Highway along I95, trips to Disney on I4, etc. Around Orlando, I seem to average 51 on the gauge

 

First 530 miles tank, computer 52.0 mpg, actual 48.6 mpg. 6.5% off.

 

Hi all. 2015 Prius Five, started driving on March 20th (11 days ago). Here is what I am seeing for MPG:
At 562 miles odo, actual mpg is 46.752 mpg
Trip meter shows 48.3 mpg.
I think that's not too bad but I wonder why it can't be more accurate? Seems like a lot of error from a car that knows exact fuel flow and exact miles driven.

[Update 4/28/15] last tank of gas, 53.8 computer vs. 50.515 calculated. Happy with the mileage; the computer sucks!

 

For a Prius Five with the 17' rims like I have with my persona, just about 47 mpg calculated is doing quite well! and a less than 3.5% variance is on the low side, so I'd say your off to a wonderful start.

 

The 17" rims throw an extra curve into the equation, since they have slightly smaller outside diameter, which means..., uhm: my head hurts.

 

Yes, they do...see this earlier posting showing *how much* that "curve" is:

Newbies - Let's See Some Pics! | Page 75 | PriusChat

 

We have 123,000 miles on our 2010 Prius. In Winter computer is off 3.5 mpg, in summer 2.5-3 mpg. Toyota knows this and refuses to correct this after nearly 6 years the 2010 Prius has been out. Let see if this continues with the 2016 Prius, if and when we ever see it....

 

Yup! 5-7ish % variance. Just like I have been showing. I've noticed with the warmer weather these last few weeks the variance on my last tank was 6% as opposed to the normal 7%+ over the winter months.

I was planning on taking my Grill Blocking off a couple weeks ago but it got cold again these last few days...

 

Just drove to Seattle and back. Carefully tracked fuel and distance. Here are the numbers:
Total trip: 428 miles odo
Total fuel used: 10.589 gallons
Actual MPG: 40.419
Indicated MPG: 43.1 - That's about 6.6% optimistic, disappointing (not the mileage; that is amazing. The amount of error sucks).
Conditions / elevation changes: typical Eastern Washington in April. 20+ mph headwind all the way to Seattle; no wind on the return. 2600' elevation change both ways. Temperatures between 40 and 60 degrees. All freeway, 60 mph average speed indicated. No attempt to hyper mile etc. just kept up with 70+ mph traffic. I think this is simply amazing. My Honda Pilot would have gotten about 16-18 mpg for the same trip, if that. Total gas $28.02.

 

I have 2100 miles on my 2015 Prius two. I just discovered that the trip meter shows me mpg for the trip. I reset trip 1 each time I fill, but keep trip 2 as a running tally. My last tank showed 48.2 mpg, but I caclulated 45.7. The running tally shows about 45.9; expected since there's been a bunch of unseasonably cold weather (single digits).

 

I would like to join in on calculating mileage, I've always done it on all my cars throughout their lives. I just filled my tank for the first time, and the automatic calculation had not been turned on when I got the car from the dealer. When I turned it on just after filling the tank and before leaving the gas station, I was surprised at the current reading which was 34mpg! I am not sure how this works. Will the car automatically calculate on a continuous basis. It has always been my habit to use the trip counter to track miles driven between fill-ups, but when I pressed the trip counter, that is when the mileage info started to display. So, if I zero the trip counter everytime I fill up, will that zero the mileage data too? How do you want the FCD taken?

 

Heh, I used to work on very high end aircraft fuel gauging systems. Using advanced capacitative techniques with multiple probes and very complex signal processing, plus careful calibration you can get down well below 1% error in liquid level sensing. With the sort of uncalibrated and unmaintained systems using a single sensor you're very lucky to hit 2%, and many systems aren't better than 10% accurate. Likewise flow metering isn't astoundingly accurate either. Given that the car probably has less than a 98% accurate idea of how much fuel its used, AND its also probably got some amount of odometer error (I know speedometers typically vary as much as 6%, not sure about odometers) I'd be pretty surprised if you got better than 90% accuracy from the car's calculations. I'm guessing they just do some basic calibration in the factory and that the software is biased towards overestimating rather than underestimating, since probably most owners won't bother to confirm their mileage and there will be less complaints that way.