Car Computed MPG vs Actual MPG

[Bob Cooke]

Hello Gang, :) First time poster. I apologize in advance if this topic has been discussed before. I've tried to search and didn't find what I was looking for.

So here it goes. I have a 2015 Fusion Hybrid Titanium, I have filled the tank 3 times now. To say I was disappointed in the results would be a bit understated.

 

My first tank I managed to eek out 344 ;( miles until the low fuel light came on. Now I can only blame myself for this. After much reading here on the forum I have seen the error of my ways. Using the remote start morning and night because the temps. Done no issue. Live and learn right?

 

The next 2 tanks were 471 and 525. Not too bad, much closer to what I expected. Now here is what isn't sitting well with me.

 

The difference between the car computed mpg and the actual mpg was off 1st tank by 35%, the 2nd tank by 12.5%, and the 3rd by 28%.

This led me to believe I was an awesome new hybrid driver, NOT the case. Once the truth was told.

31.6 vs 42.6, 43.4 vs 48.8, 41.7 vs 53.4.

 

These numbers are way too far off for me to think that this is a built in error. Anyone else have any experience with this issue?

I can accept the numbers not being spot on and maybe off a couple of percentage points but this is beyond ridiculous.

I would like to arm myself with as much ammo as I can before marching into the dealer and demanding something be adjusted.

 

Any help would be much appreciated.

Bob

 

[Texasota]

Your actual MPG is probably not unreasonable given where you live (i.e. cold winter conditions).

 

My actual MPG vs trip display MPG varied a lot for the first several tanks. I have been keeping my data on a spread sheet for the ~9000 miles I have on my 2015 and, on average, the trip display is inflated by about 2 MPG. But I still get a lot of randomness in the amount of over reporting and under reporting by the trip display. I recently had one that inflated the actual MPG by 8 MPG which surprised me.

 

I think this car is very sensitive to the slope of the pavement at the fuel pump. Seems to be more sensitive to that than other cars I have owned.

[md13ffhguy]

The calculated result is affected to the greatest by the denominator - fuel used (or in the case of a manual calculation, pumped). It will vary. Your tank is not like a measuring cup where you set it on a level surface and fill it to a visible line. We really don't know how accurate each pump is, nor do we know exactly how far we end up above or below that invisible full line. A half gallon variance can affect the result +/- 2-3 MPG.

 

I've been meaning to post some thoughts about this same subject based on my own collected data. Maybe tomorrow.

[Cobra348]

I can tell you from my Fiesta experiences that the car computer isn't anywhere as accurate as one would think. Figure your tank MPG from the gas receipt for best results. Also, as pointed out already the first few tanks will be whacked as the car "learns".

[lolder]

You probably need to average 10 tanks even if you use the same pump every time. Then you can calculate the offset error of the car computer. You only need to do that once. After that, the computer is very precise and you can just do the mental calculation of the actual mpg. For instance, my 2010 computer reads about 4.5% too high mpg. The odometer reads 2.5% too low for a net of 2% too high. If the computer says 40 mpg, the actual is 39.2. The numbers for the 2013+ FFH appear to be similar. Apparently in the 2013+ models, any fuel used after remote start before driving is not included in the computer calculation so discard any pump calculations that include remote start operation. That is really your mpg but that won't let you calibrate the computer accurately.

Edited March 25, 2015 by lolder

[jeff_h]

You probably need to average 10 tanks even if you use the same pump every time. Then you can calculate the offset error of the car computer. You only need to do that once. After that, the computer is very precise and you can just do the mental calculation of the actual mpg. For instance, my 2010 computer reads about 4.5% too high mpg.

 

Bingo for lolder once again, first on the note about spanning multiple fill-ups, and using the same pump (not just the same station) too. His note on his 2010 being 4.5% too optimistic is about the same as my 2010 was, and about the same as the Prius before that.

[CCalvinN]

I'm in a similar situation as I've only filled my new FFH about 6 times. Only the last tank and a half have been without any remote starts, so I'm still learning what effect that has on the accuracy of the displayed MPG. On my last fill up (with no remote starting) there was only a 5% difference with the car being on the optimistic side of that equation. That 5% optimism stands with what I've noticed in most of my cars, so I expect that to remain.

 

I was shocked at how much fuel was eaten by both remote starting the vehicle and having it idle without moving. As lolder points out the fuel used during the remote start isn't factored into any calculated fuel milage. So if you're still using that, that alone could be the majority of your differences.

[Easy Rider]

 

I would like to arm myself with as much ammo as I can before marching into the dealer and demanding something be adjusted.

 

Any help would be much appreciated.

Bob

 

Are you resetting the MPG display with each fillup ?? If not, you should.

 

And I have never heard of any car maker doing warranty work based on an ESTIMATED fuel usage figure that was off.

 

41-43 is about what I am getting most of the time but the displayed figure is always 3-4 MPG on the high side.

[Cobra348]

Are you resetting the MPG display with each fillup ?? If not, you should.

 

And I have never heard of any car maker doing warranty work based on an ESTIMATED fuel usage figure that was off.

 

41-43 is about what I am getting most of the time but the displayed figure is always 3-4 MPG on the high side.

Agreed on the reset point. I learned with the current stable to reset trip, computed (average) MPG and average MPH for better readings to guess-timate from. I also found that in the '14 models I have now, the computer is .5 to 3.8 MPG over what I calculate at fillup. My prior '11 and '12 were mostly UNDER by that amount.

 

Remote start vs MPG: Usage will impact mileage for sure depending on how long the car sits idling, but if you do a lot of traffic lights, they will chew up MPG as fast or faster than the remote by itself. This is especially true if the red is a very long one. There is one particular light in town that I can see the MPG readout drop by .4 every time due to the length of the red.

 

<mutters> FFH now waiting transport ... getting itchy to have it!!

[lolder]

In a hybrid, the mpg doesn't drop at lights.

[Easy Rider]

In a hybrid, the mpg doesn't drop at lights.

Because the gas engine shuts off most of the time when you are not moving.

[hybridbear]

Are you using the advanced trip meter which shows gallons used? As others have stated, if you reset that at each tank & use a site like Fuelly it's easy to track the computer error. Check out my tanks via the Fuelly signature. I've tried to record what the car reports for gallons with each fill-up for comparison purposes.

[Cobra348]

Because the gas engine shuts off most of the time when you are not moving.

<dopeslaps self> DUH! I completely forgot about that aspect. You're right. It's the remote start fault!

[Hybrider]

My own results in my 2014 FFH for the difference in gauge versus calculated MPGs for each fill-up have been all over the map (most recent fill-ups shown in table below), even when filling from the same pump at the same station.

 

The "Pump" column below shows the pump number followed by the encoding of the cross-streets where the filling station is located. In the not-so-distant past, I have been much more consistent in using the same pump at the same station for many, many times in a row, back when the gas prices weren't changing so drastically from fill-up to fill-up, but the differences between my gauge and calculated MPGs at the same exact pump were still all over the place.

 

Pump Trip Gauge Calc'ed
---- ----- ----- ------
15lb 270.0 54.8 50.6
15mv 218.4 52.3 51.5
15pu 240.1 53.1 48.4
15mkcc 277.4 56.1 52.0
15mv 277.3 55.9 59.5
15pu 268.0 55.5 48.3
15pu 297.9 57.4 55.3
15pu 278.9 56.5 53.6

[Bob Cooke]

WOW quick response from everyone thank you. I now realize that the first tank was off due to the remote starting fuel not being accounted for. I understand this

and can accept the 35% error. However the next 2 tankfulls did not have any remote starts. I would be happy if my mpg readings were off by a couple of mpg, But

to be off by 12.5% and again 28% is too much. I have tracked my fill ups on Fuelly and will post it when I figure out how to include it. I will try and use the same pump

at the same station for the next few fill ups to address any randomness from other pumps and stations. Please keep in mind I really like the car so far. Just trying to see

if a problem exists that needs a dealers attention. Hopefully this will sort itself out sooner then later.

I have reset the trip and MPG reading at each fill up. so that should not be the issue.

My car does not report fuel used like some others here have shown, not sure if they removed that option from the 2015's

But if the computer MPG doesn't get closer to reality they might as well remove it from the dashboard. I'll take no MPG over really optimistic MPG.

 

Thanks

Bob

Edited March 25, 2015 by Bob Cooke

[Texasota]

My car does not report fuel used like some others here have shown, not sure if they removed that option from the 2015's

It was removed on the 2015s.

[hybridbear]

It was removed on the 2015s.

Removed from where? The Trip Summary? The Advanced Trip Meters?

[Texasota]

Removed from where? The Trip Summary? The Advanced Trip Meters?

I don't think it is displayed anywhere. I have not found any display that shows fuel used other than the fuel tank gauge/graphic. And to the best of my knowledge I don't think the 2015s have an "advanced trip meter".

[hybridbear]

I don't think it is displayed anywhere. I have not found any display that shows fuel used other than the fuel tank gauge/graphic. And to the best of my knowledge I don't think the 2015s have an "advanced trip meter".

You can't do what shown in this video?

[Texasota]

You can't do what shown in this video?

No, I have tried this before and I don't think the standard/enhanced option is available on the 2015s. I also just verified that the standard/enhanced option is documented in the 2014 owner's manual but has been removed in the 2015 owner's manual.

[hybridbear]

No, I have tried this before and I don't think the standard/enhanced option is available on the 2015s. I also just verified that the standard/enhanced option is documented in the 2014 owner's manual but has been removed in the 2015 owner's manual.

What all is shown on your trip meter? Do you have an options to change it?

[Texasota]

What all is shown on your trip meter? Do you have an options to change it?

What is displayed in Trip 1 or Trip 2 is just as the owner's manual documents:

 

 

Trip 1 & 2

Provides trip odometer, trip average fuel economy and trip timer. Distance traveled on battery power only with the engine off is shown in blue next to total trip distance

 

I just tried to change it again today and when you push the -> button (while trip 1 is displayed) on the left side steerig wheel controls the only option is "help". No other options to change it are listed. I'm confident this feature was removed on the 2015s along with all data on gallons of fuel used.

[hybridbear]

What is displayed in Trip 1 or Trip 2 is just as the owner's manual documents:

 

 

I just tried to change it again today and when you push the -> button (while trip 1 is displayed) on the left side steerig wheel controls the only option is "help". No other options to change it are listed. I'm confident this feature was removed on the 2015s along with all data on gallons of fuel used.

That really stinks!! Can other 2015 owners confirm? I want to make sure this isn't just on the Hybrid S like you have.

[Cobra348]

Haven't got a car to confirm with but according to the Owners Manual PDF I have it states

 

Note: The trip data, and average fuel
economy cannot be reset in MyView.

 

Page 98 - regarding information displays. Nowhere else can I find any indication of how to reset trip data. Apparently the MyView info display is the only spot I see where you can show Trip 1 and/or 2 at all.

Edited March 30, 2015 by Cobra348

[Texasota]

That really stinks!! Can other 2015 owners confirm? I want to make sure this isn't just on the Hybrid S like you have.

Confirmation from other 2015 owners would be a good thing to confirm I am not missing something or that it is peculiar only to the Hybrid S. But, given that the documentation was removed from the 2015 owner’s manual I doubt if it is Hybrid S specific.