Observations of displayed vs calculated mpg's

Just curious what was your theory again ??

You had a question on milder weather better MPG that is correct in genearal.

The 4% error is correct MFD (i.e. car computer) overreport the mpg somewhere 4-5% but remember you can have a few percent error at the gas station ... but that is random.

What many of us found and was long treads about 3 years ago that the MPG by the car is BIASED .... I had 2004 prius ketp record the MFD was reporting very very accurately and it was random 1% or -1% .... conclusion was that fill up errors was almost the same.... I could leave in the 2004 let say 10 fill up and calculate and the car reported mpg was within 1% !!! So many of us was pretty surprised how toyota could screw this up this badly (and was hoping for a while that a software upgrade can fix it) ... I am curios if the 2012 version which had some tinkering ... maybe more accurate ....

Cheers

 

My 2012 is running about 1% less inaccurate than my 2010 was at the same distance. Considering the variables thrown into the mix, this is still indistinguishable from 'no change'.

 

What do you mean by the same distance ??? Distance shouldn't really impact mpg directly.

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Sorry do you mean the mpg is 1% -less so running 3-4% (over) or you mean the inaccuracy which is the error is 1% less (that would make it 4.95%-3.95%

But I agree 3-4% in this type of application especially when it is biased just way too high ... Because remember this is not simply inaccurate measurements that would go both ways this IS NOT.

If mileage (odometer) would have this much systematic error it would make over 500 miles a year for me ... people would be screaming. (Of course putting the wrong sized tire CAN indeed make that happen).

 

My 2011 runs 4-5% off from the display to actual fuel usage.

 

The 2012 has only 5k miles on it, so I compared to only the first 5k miles on the 2010.

My 2010's display error averaged 4.9% over the first 5k miles, but grew to 6.6% over the nearly 37K I put on it before trading it in.

I didn't reset the 2012's trip meters immediately to align it with the dealer's PDI refill, so a prior test drive or two is not properly accounted for. But the error so far seems to be about 4%.

Commuting hypermiling with many gliding ICE on/off cycles seemed to create more error than long highway runs. The 2012 has had no commuting, with most of its miles run up during a single major road trip.

Fortunately, odometers don't have this much error anymore. (I received the odometer error class action lawsuit notices for two previous brands of cars. Both settled by extending the warranty mileage by 2%, though neither of my cars were off that much.) My 2010 read 0.2-0.3% low, not high, at 20k miles. This 2012 is closer of 0.1% low, but has not yet been as rigorously checked. It also has a different tire make/model than the earlier car.

 

OK I got it .... but still curious how it went up the overall ... but my stats show something similar ... now I am 5.59% for just over 37k (maybe the wearing of the tire affecting this ??? ... ) But the very little of tire wear couldn't not be more than 1% (should be even less). but my average trip error grew as well!!!

Again very interesting ... that was my starting point actually a little bit more

My driving situation is quite the opposite the driven miles at least 90 percent daily or weekend commuting. The few "roadtrips" were all less then 200 miles one way ...

This is also very informative ... I was aware of the odometer lawsuit but did not know any specific .. this is why I brought it up. I remembered that the ODO MUST have been quite accurate unless owner doesn’t comply with tire spec...

by the way SGe I have had quite a big errors out of the box actually seemed to mirror the car mpg ... ... in other words what was reported to distance as mile was just about 5% or even more higher then ODO or GPS ... (I wrote about this in PC) but SG advised me to do adjustment (which you can do ...) and then SG mpg was within 1% to my calculation ... (I adjusted over about 10 trip comparing to gps). I just do not know what to make of it ....some of the data coming on the data bus is just skewed ...

Thanks for the information ... I do not have any plan for now to get a 2012 .. if i can affored will go for PiP

 

Here are some numbers some of you might find interesting -
The differences in the displayed mpgs in our 2010 Prius model 5 and the calculated (miles driven per tank divided by gallons to fill tank) seems to depend on displayed mpgs. Typical snapshot numbers:

Warm, calm days, displayed mpg - 56, calculated mpg - 52.5, difference - 6.25%
"Average" driving conditions, displayed mpg - 52.5, calculated mpg - 50.0, difference - 4.76%
Cold, nasty days, displayed mpg - 45, calculated mpg - 43.5, difference - 3.33%

By difference I mean (displayed-calculated)/displayed. Anybody else notice this, or am I slicing/dicing things a little too fine?

 

Hello neighbor. My CTh (a G3 Prius in a Lexus body) shows similar errors. Mean is about 4.6%.
This Google Doc shows about 5k miles worth of fill-ups.

 

I didn't know you were averaging 53 mpg with your CTh. That probably has to be an equivalent of mid to lower 60's on a Prius, right? That is amazing!

 

We have a G2 Prius too. I used to scrape 60 mpg overall for my my long distance driving, now done with the CTh.
I do not consider it an outrageous result, since it is relatively easy to duplicate. E.g., Justin (F8L) beats me handily. The other thing to know is I drive at around 5-7k feet altitude, and this gives me a significant fuel economy advantage in highway driving.

 

I can not back that up... although I do not drive my car on long trips ... but when I did (2/3 times) I did not find any significant difference ... BUT I did not drive FULL tanks only long distance highway driving ...

So if someone has this data please share with us. This would be interesting ...

But Bob and others found that bias is almost constant ... my observation is the same with my driving ...

 

I do not see this over 3 years of data ... I see errors in that range but I do NOT see it by that trend. Please note that 1-2% could be easily by just the fill up error .... I analyzed my data extensively I do not see this trend over 3 winters.

I define the error the same way. How many data point you have? My "feeling" but no proof of any kind is this more depend on average speed over the tank... but even that not consistent ... and that would make sense since more you drive around 50-65 steady the efficiency would stay more at the same range. Anything out of that range is wildly varies .... sob Bob writes ups

 

On my 2012 Prius (Canadian model), if I cycle through the menu through the trip button, I get to a "settings" menu and then when I long press, I can set a few options one of them is the calculated consumption. Would the car in this case use this value for calculation instead of what it thinks? i.e will it offset the reported vs calculated fuel consumption?

 

Interesting noone has shown this ... I do not know but maybe this is where you can calibrate ??? You coudl try ... and maybe the MFD gets a little be more accurate ...currently is way out the reality ... 5-6% always positive .. I would rather have a 2% +- gauge then this baised one...


Let us know ....so far 2012 users report same +5% bais...

cheers

 

I will calibrate it at the next fuel up ( in 10 days ) then will monitor afterwards.....the first flip, it said 4.5L/100km and I calculated 4.6......second 4.3 and still calculated 4.6.......perhaps with the user input, this will get better

 

On my settings menu there's a "comp. consumption." Is that what you're seeing?

I think that just allows you to enter the MPG of a different car, so you can compare your fuel savings in your Prius vs the other.

 

Ahhhh....so it is not a calculated value.....well gee that's pretty darn useless....at least to me