"Your mileage will vary"

[ivymike]

I have a 2012 Ford Edge Limited with 3478 miles on it. The EPA fuel mileage sticker puts the fuel economy at (cty/hwy) 19/27 mpg. My experience has been very different from that, and I'm wondering whether this is something that is likely to resolve itself, or if the mileage estimate is simply WAY wrong for the vehicle.

Below are my records of mileage and fuel economy since purchase:
date odometer gallons [mpg tank]
21-Apr-12 280 0.000
27-Apr-12 482.6 12.250 16.5
1-May-12 746.9 14.236 18.6
7-May-12 916.5 10.410 16.3 17.3
11-May-12 1120.7 12.969 15.7
14-May-12 1365.2 13.616 18.0
21-May-12 1594.3 12.183 18.8
30-May-12 1803.3 13.114 15.9
06-Jun-12 2022.5 13.061 16.8
11-Jun-12 2212.2 12.226 15.5
16-Jun-12 2437.1 13.969 16.1
22-Jun-12 2613.4 12.230 14.4
02-Jul-12 2797.6 13.491 13.7
07-Jul-12 2955 9.553 16.5
08-Jul-12 3131.7 8.696 20.3 (purely hwy)
08-Jul-12 3294 6.723 24.1 (purely hwy)
14-Jul-12 3477.5 12.256 15.0

I have been using 87 octane fuel, as per the recommendations of the manual, and I have not been driving in any particularly interesting fashion, save for the tank consumed on 08-Jul-12 where I drove the entire time on cruise control at speeds between 55 and 70 mph (depending on the local speed limit) and managed to get 24.1 mpg. The rest of the driving is suburban, with a mix of highway and medium-distance stoplight driving (40mph+ speed limits are typical in our neighborhood)

The speedometer reading precisely matches GPS readings of speed, so I assume that the odometer is also calculating miles correctly. The tires are properly inflated (actually 1 psi higher than what it says inside the driver's door frame, or 33.5 psi).

So what gives? I can't get 27mpg out of the vehicle unless I drive at a constant 40mph on flat ground (and then it says I'm getting about 27.8)! What cycle would I possibly drive it on to average 27 mpg highway?

 

[GregLocock]

That does seem quite a difference.

Typically the fuel consumption in my Fiestas improves by 10% over 5000 miles, probably due to the diff wearing in. How much ethanol is in your fuel? 87 octane sounds very low to me, but then I think that USA might use a different grading system to Oz.

Which engine do you have? If you have the 3.5 then 17-20 mpUSg sounds about right to me.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[ivymike]

It is the 3.5, w/6-spd automatic

 

[IRstuff]

There's some pretty interesting comparisons of label vs. actual in this report:

http://www.epa.gov/fueleconomy/420r06017.pdf

One major difference, I think, is how the whole acceleration phase is worked. According to my usage meter on the Prius, the acceleration phase generally sucks up a sizable chunk of one's mileage. Given that most car mileage labels are actually self-reported, it's likely that the testers are trained to optimize their accelerations and decelerations to maximize mileage. Since we, as typical drivers, are not trying to perform mileage tests on a daily basis, our driving habits are probably radically different than those of the testers.

TTFN
faq731-376

 

[IRstuff]

And there's every likelihood that the variability of actual mileage, even with optimized testers, is still quite high. a 20% variance would not necessarily be surprising.

And, of course, no car company is going to use a low mpg car for their official testing...

TTFN
faq731-376

 

[ivymike]

Hmmm, I had thought the figures were based on test cell testing rather than road testing, with everything programmed...but I never really investigated.

My actual mileage in my 2012 Taurus matches the EPA figure precisely.

 

[ivymike]

A weird thing about the edge was that the first couple of tanks were at about the right mileage, then it trended down from there...

 

[DRWeig]

If it did good but is tapering down, and you haven't changed driving habits, it's worth investigating.

My Chevrolet HHR did super when I lived in Memphis, but mileage went to pot after move to Atlanta. Lots of time idling or going less than 10 mph in traffic jams. It still comes close to the EPA number on the road, though.

Good on ya,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[GregLocock]

Oh, in town the mileage can be out by heaps. I've seen identical cars get 50% variation depending on driver, in town, so its the highway result that is the puzzle.

Another thing is did you get the base tire, or did you go for something a bit chunky?

Yes, these ratings are from a self certified roller dyno test. The EPA checks about 15% of them. The drivers used to be very good at lagging on the accels and so on, I imagine now its all done with robots.




Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[IRstuff]

OK, I wasn't sure whether it was dyno'd or not. If dyno'd, then wouldn't actual mileage drop because of aerodynamic drag?

TTFN
faq731-376

 

[GregLocock]

No, because the resistance curve of the dyno is based on real life coastdown tests, which have the aero drag in them.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[GregLocock]

Actually cancel that, I have a horrible feeling they don't use proper electic dynos, otherwise what is all the fuss about inertia weight categories? Hmm, sorry I don't know. I'll be talking to a powertrain guy next week, I'll try to remember to ask him.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[ivymike]

I got the wheel/tire that came on it (all at the dealership save for the sport model had the same) ... but the wheels were a bit gaudy (chrome ). 245/50R20...

 

[TonyDeRamo]

Hmm that seems way off. I'm getting about 3-4 mpg more than the sticker said in my 2011 Ranger in both highway and residential driving. It is a 4 cylinder and manual transmission, however. I just hit the 10k mile mark.

"If You Can't Find Anything To Live For Then You Better Find Something To Die For."

 

[dgallup]

I get almost exactly the EPA rating in my 350Z. I can even get a little better than the highway rating in the spring or fall.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[mattsooty]

You could take it to somebody with a scan tool and ask them to check the fuelling adaptations (aka long term fuel trims). These do exactly as they say on the tin and correct the fuelling in the rich or lean direction - giving the actual closed loop lambda controller less work to do to keep the charge at stoich.

I have seen numerous vehicles is a small air leak that is not sufficient to flag up an error but enough to alter the fuelling with associated side effects.

I would also have thought that, with aforementioned scan tool, you would be able to find out the torque adaptations. In a similar vein to the fuelling adaptations you might find that you have a 'tight' engine - but not quite enough to flag a fault.

MS

 

[RossABQ]

It might be worth disconnecting the battery to reset the learned adaptations, i.e., set it back to the way it came off the showroom. If mileage goes back to the earlier better numbers, something is surely amiss.

 

[MiketheEngineer]

Don't let your wife or daughter drive it!!

 

[ivymike]

@MattSooty: I imagine I can get that done down at the Autozone parts store with their in-store scan tool, good idea.
@Ross: I'll try that too... but I expect my wife will be upset with me when the radio presets disappear!

 

[LionelHutz]

It seems to me the the newest EPA testing actually represents real world driving conditions moreso than the older test methods. Still, this sounds further off than most. Accelerating the mass is a large user of fuel. Trying to limit the acceleration rates and keeping a constant speed can help.

Resetting the long-term fuel trims in the computer is fairly pointless. The computer uses short term fuel trims to keep the correct mixture and these adjust within seconds at any particular operating point, with the long term fuel trims following shortly after.

The Canadian window sticker would read 24/36...