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Discussion Starter · #1 ·
I have seen many references to the Average MPG display being wrong because the Odometer reading / gallons replaced equals a lower figure.
The issue here is that you cannot assume the odometer is accurate anymore than you can assume the Average display is wrong.

Testing is the only way to resolve the issue and that has already been done. The results show the Average display is accurate based on it over-reporting by 2% while the odometer under-reports by a little more than 2%.

From a number of long distance drives performed in the 2011 and 2012 Hyundai Sonata Hybrid, we have shown that the aFCD (averaging fuel consumption display) over reports by 2.0% compared to fuel consumed over odometer miles traveled. Opposing that over report, the odometer/Trip A/B under reports miles traveled by slightly more than 2.0% leading to an overall slightly pessimistic display vs. actual fuel economy. In other words, you receive slightly more mpg than the display reveals.
Hyundai: Real World Fuel Economy Improved To Meet Expectations, Not a Window Sticker - CleanMPG Forums
 

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Maybe for the single car tested for the article. But I have 90 tanks and over 50,000 miles worth of data that state otherwise on my 2011 - even with the odo correction. For my car the aFCD is consistently 5% - 10% above actual/calculated. Below is my fill up from this morning which is typical for most of my tanks. Mileage is from the odo (uncorrected).

528.0 miles, 13.54 gallons, 39.0 MPG, (aFCD indicated 43.7 MPG)

Even with a 3% odo correction that only takes the actual MPG to 40.2 - nowhere near the 43.7 average MPG indicated on my dashboard. Granted this is only one tank and the pump can add to the variation. But all 90 of my fill ups have been this way where the aFCD is over estimated like this - not a single one the other way.

Not saying all HSH's are like mine - only speaking for my car personally. Would be interested to see what others who are tracking and calculating actual MPG (over numerous tanks) are getting compared to aFCD indicated.
 

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I've only filled up twice, but I'll let you know about mine soon. Mine seemed to over-report about 2MPG (46 MPG reported vs 44 actual).
 
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Have been at an average mpg of 36.7 and have not reset since several fill ups. So if the average is allowed to remain constant and not be reset at fill up it might be more consistent. Oh and a quick note, mine is indicating lower average mpg but have been doing 600+ with 13-14 gallon fill ups.
 

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Discussion Starter · #5 ·
Maybe for the single car tested for the article. But I have 90 tanks and over 50,000 miles worth of data that state otherwise on my 2011 - even with the odo correction. For my car the aFCD is consistently 5% - 10% above actual/calculated. Below is my fill up from this morning which is typical for most of my tanks. Mileage is from the odo (uncorrected).

528.0 miles, 13.54 gallons, 39.0 MPG, (aFCD indicated 43.7 MPG)

Even with a 3% odo correction that only takes the actual MPG to 40.2 - nowhere near the 43.7 average MPG indicated on my dashboard. Granted this is only one tank and the pump can add to the variation. But all 90 of my fill ups have been this way where the aFCD is over estimated like this - not a single one the other way.

Not saying all HSH's are like mine - only speaking for my car personally. Would be interested to see what others who are tracking and calculating actual MPG (over numerous tanks) are getting compared to aFCD indicated.
First: The article wasn't based on a single car. It was at least one 2011 and one 2012... I will admit a better test would be several of each but this is all we have.
Second: My main point is we do not know the Odometer is correct so to call that calculation the "Actual" is a mistake.
Third: My own observation after 37,200 miles shows a 3 - 5% difference in odometer/gallons used vs. aFCD which looks accurate if you consider 2% over on aFCD and >2% under on odo/gallons = >4% difference .
Lastly: I'm sure you are correct about your car showing bigger differences but in general the aFCD is very accurate!

Thanks for weighing in...this is what makes a forum interesting to read.
 

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Wayne Gerdes from CleanMPG spends 15-60 minutes filling the cars gas tanks to the top to get exact measurements. So you can be assured that they are accurate.

 

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Discussion Starter · #7 ·
Wayne Gerdes from CleanMPG spends 15-60 minutes filling the cars gas tanks to the top to get exact measurements. So you can be assured that they are accurate.

Right you are Tom...Wayne has my trust 100% that he is honest and accurate in all of his measurements. That is why I posted the article (as proof) from his CleanMPG website!
 

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I travel frequently for work and get very bored while driving. To keep myself from going nuts I've calibrated my odometer with both highway mile markers and gps many, many, many times (yes, I know I'm a bit OCD). The gps and mile markers always match or are extremely close, within a few tenths, over mutliple 50 to 100 mile runs. My odometer is consistently 2.5 % and more so lately 3.5% under both the gps/mile markers.

So yes I do know the accuracy (actually the inaccuracy) of my particular odometer. I also know that the inaccuracy increases as your tires wear and get smaller. My tires are approx 3/8" smaller OD due to tread wear (my tires are ready to be replaced btw) which changes the revolutions per mile from 766 when new to 775 revs per mile in their worn/current state. That alone adds an additional 1% to the odo error which explains the 3.5% error lately.

I also understand the variation of pump fills from one tank to the next. But if the aFCD difference from calculated was only due to tank fill variation, I would have roughly half of my calculated tanks on the high side of aFCD and half on the low side - that's the way statistical variation works. And the average of those 90 tanks would equal the average of all the aFCD figures. That hasn't been the case, not even close on my car as I haven't had a single tank where the aFCD was under the calculated figure even with a 3% odo error adjustment. That said I admit I've had a few out of those 90 tanks that were very close after adjustment for odo error.

I too trust the data Wayne gathers on the cars that he tests - because he isn't just blindly reporting aFCD without verifying accuracy on that particular car. He's scientifically calculating actual MPG based on very accurate fills and actual GPS or corrected odo miles. So I wouldn't call Wayne's calculation method a "mistake" if you know odo accuracy or are using GPS (or both).

Again - I'm not saying this is a universal HSH issue - just my car.

All that said I agree that the aFCD is in the ballpark and close enough for normal, sane, non OCD types of people! :D Maybe after I get the update mine will be more accurate? We'll see!
 

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not just you

I travel frequently for work and get very bored while driving. To keep myself from going nuts I've calibrated my odometer with both highway mile markers and gps many, many, many times (yes, I know I'm a bit OCD). The gps and mile markers always match or are extremely close, within a few tenths, over mutliple 50 to 100 mile runs. My odometer is consistently 2.5 % and more so lately 3.5% under both the gps/mile markers.

So yes I do know the accuracy (actually the inaccuracy) of my particular odometer. I also know that the inaccuracy increases as your tires wear and get smaller. My tires are approx 3/8" smaller OD due to tread wear (my tires are ready to be replaced btw) which changes the revolutions per mile from 766 when new to 775 revs per mile in their worn/current state. That alone adds an additional 1% to the odo error which explains the 3.5% error lately.

I also understand the variation of pump fills from one tank to the next. But if the aFCD difference from calculated was only due to tank fill variation, I would have roughly half of my calculated tanks on the high side of aFCD and half on the low side - that's the way statistical variation works. And the average of those 90 tanks would equal the average of all the aFCD figures. That hasn't been the case, not even close on my car as I haven't had a single tank where the aFCD was under the calculated figure even with a 3% odo error adjustment. That said I admit I've had a few out of those 90 tanks that were very close after adjustment for odo error.

I too trust the data Wayne gathers on the cars that he tests - because he isn't just blindly reporting aFCD without verifying accuracy on that particular car. He's scientifically calculating actual MPG based on very accurate fills and actual GPS or corrected odo miles. So I wouldn't call Wayne's calculation method a "mistake" if you know odo accuracy or are using GPS (or both).

Again - I'm not saying this is a universal HSH issue - just my car.

All that said I agree that the aFCD is in the ballpark and close enough for normal, sane, non OCD types of people! :D Maybe after I get the update mine will be more accurate? We'll see!

I've done the same in the 2011 and 2012 hybrid I traded up for. Now wish I waited but I didn't. Measured odometer with gps and mile markers and even with 10 miles its obvious the odometer is off like you say. Good for us as it makes are 100,000 mile warranty last another couple thousand miles.
 

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I know that years ago the speedometer was fed by a cable from the transmission to provide you with the speed. Now I would assume that it is all electronic based upon how many times some component passed by a sensor and then feeds this information to a computer. If this is the case then the calculation should be electronic. If this is the case then why can't the software calculation be modified to reflect a more accurate reading?

I"m sitting at roughly 66000 miles on my car now. If the speedometer and odometer are off by 3% then my odometer is off by around 2000 miles. Is 3% considered an acceptable deviation for our cars?

To me it sounds like it is a software issue since almost all of us are experiencing the same deviation all the way across the board.

Chuck
 

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I know that my 2012, post update, was reporting a solid 7-8 mpg higher than my manual calculation between fill-ups. This was across a 2000 miles vacation trip and every fill-up had similar discrepancies.
We're going to actually log the on-board avg vs phone app log calculations and see how drastically off the on-board is for multiple tanks.
Im curious how high of a discrepancy would warrant arguing warranty service.
 

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I know that years ago the speedometer was fed by a cable from the transmission to provide you with the speed. Now I would assume that it is all electronic based upon how many times some component passed by a sensor and then feeds this information to a computer. If this is the case then the calculation should be electronic. If this is the case then why can't the software calculation be modified to reflect a more accurate reading?

I"m sitting at roughly 66000 miles on my car now. If the speedometer and odometer are off by 3% then my odometer is off by around 2000 miles. Is 3% considered an acceptable deviation for our cars?

To me it sounds like it is a software issue since almost all of us are experiencing the same deviation all the way across the board.

Chuck
They are probably doing us a favor by giving us an extra 5-6,000 miles on our 100,000 warranty and by fewer speeding tickets.

On my Santa Fe if I put CC at 60 mph the Garman says I'm going 57 mph.
 

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Eric1r - I purchased a 2013 Sonata Hybrid 5 weeks ago. I have filled up six times and the display is consistently 9 - 10 % higher than the actual calculated consumption. I have brought this issue up with the local Hyundai and they are supposedly going to research the issue. This is not due to odometer errors, as I verified mileage accuracy over the course of two 500 mile trips.
 

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I've had an accurate reading one time. It's generally 2 mpg higher than actual and with yesterday's fill up, 4 mpg off. It's a nice guide but nothing to attach accuracy to.
 

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When Chris, a friend of Waynes told me to use the 1.033 X my total mileage on Trip "A" I was also adding one extra gallon to my tank. I know based on the challenge that Wayne and Chris took a couple of years ago with the 2011 Optima Hybrid, the tank can hold around 22 gallons, but I've never gone above one extra gallon. For example when I get ready to fill up and trip "A" is showing let's say 530 miles, I will X that by 1.033 and get 547.49 then divide that by the total gallons used to include the extra gallon, I found the difference is sometimes lower than the aFCD is showing by 2-3 miles per gallon.
I plan on trading in my 2011 for a 2014 and was wondering will I have to continue using the 1.033 to get the better average?
 

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Well I still get chappy mpg. Less than 36 I drove from vegas to Tucson cruise set at 70 got 36.4 per dash computer. My car has 3,500 miles and my tires still lose nitrogen. Been back 3 times no leaks planet hyundai says. I left with 35 psi, when I was ready to leave I had 21 psi. This time used air came home my dash says 25.7 mpg? I'm now makei n get my 4th visit to the stealer next week stay tuned.

Sent from AutoGuide.com Free App
 

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No hybrid, but my computer usually reads 4 mph over odo/gals. The speedo reads 2+ mph high at 60. With my TDI Beetle, the common knowledge was that the speedo ran high cause of euro laws about speedo readings over a range of tire sizes; the odo was correct with stock tires.

I guess I'll try to verify odo against mile markers next time I go on a trip. I don't trust the vernon for distance covered.
 

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No hybrid, but my computer usually reads 4 mph over odo/gals. The speedo reads 2+ mph high at 60. With my TDI Beetle, the common knowledge was that the speedo ran high cause of euro laws about speedo readings over a range of tire sizes; the odo was correct with stock tires.

I guess I'll try to verify odo against mile markers next time I go on a trip. I don't trust the vernon for distance covered.
I did this with my gps and found the car was 1.8% low. Meaning, you drive 100 miles and the car reports 98.2 miles driven.
 
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