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Actual vs Indicated MPG

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Old 07-31-2015, 05:07 PM
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Actual vs Indicated MPG

Some of you know that I've been critical of the "indicated MPG" that our trucks show. In fact, I have borrowed the term Lie-O-Meter from another FTE'er to describe the indicated reading and my contempt there for. But, you may be wondering why I'm up in arms about it, so here's why.

I"ve tracked every drop of fuel that's gone into the truck save for the initial fill that the dealer did. And here's what I'm seeing:



As you can see, the error is getting worse and is up to almost 8% of the actual reading. Unfortunately I haven't been capturing the LoM's "gallons used" to compare that the the actual usage, but I will in future as it will be interesting to see if that's where the error is.

So, I'm hoping that we can use this thread to capture the actual vs indicated MPG from others. However, if you aren't capturing the info for consecutive tanks then it may not be accurate since it is quite possible to overfill the tank one time and underfill it the next and heavily skew the MPG.

So, what'cha got?
 
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Old 07-31-2015, 05:45 PM
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I compare the gallons used on the display with gallons added during the fill up, every time.
1% error is what I generally see over 45,000 miles. Occasionally 2%, but generally just 1%. I add 25 gallons, it says I used 25.3 or thereabouts.

As my speedometer seems to be very accurate for the speeds I generally drive,
non stop highway at 55 to 65, I see that factor of the milage calculation to be right on.

So, as my summer milage reading is generally something like 21.4, my 1-2% error
gives me, what I feel, is an honest 21 mpg, which I've gotten from day 1, the last 3
years, during the warm months.

If you just wanted 2015 truck results, please disregard after "I compare……"

2012 4WD Eco 3.31 gears no packages
6000 Ft, mountain highway driving up to 7, down to 4 up to 7 down to 6000
That kind of highway driving
 
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Old 07-31-2015, 05:57 PM
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I doubt the errors are only with the 2015 trucks, so appreciate your input. And, I'd be happy if mine were off only 1%.
 
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Old 08-01-2015, 05:09 AM
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This is so subjective in how we drive, pump and even where we consistently purchase fuel. When the fuel pump shuts off, then technically your tank is full and you shouldn't add anymore gas. Some people will continue to add fuel thinking they are filling the fill pipe and all they are doing is hurting the system.

Mine has been very consistent as well. No frills 2011 XLT 4x4 with ecoboost and 3.31 axles.
 
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Old 08-01-2015, 07:49 AM
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Tim - I agree that the MPG we get is subjective, but not the variance between actual and indicated MPG when measured over consecutive tanks. If I over or underfill on one tank it will show up on the next as noticeably better actual MPG than indicated MPG. But in my case the difference between actual and indicated is getting worse.

You may notice that I haven't complained about my actual MPG in this thread. While I'm not pleased with it, I'm trying to keep this thread to a discussion of the difference between actual and indicated. But, as said in the first post, "…if you aren't capturing the info for consecutive tanks then it may not be accurate since it is quite possible to overfill the tank one time and underfill it the next and heavily skew the MPG."

When you say "Mine has been very consistent as well", does that mean you have tracked your actual per-tank MPG over several tanks and find that it tracks closely with the indicated MPG? I'd really like to see what others have recorded so I can compare it to mine, and am quite willing to put the info in a spreadsheet for you/them if you'd like so we can compare apples to apples.
 
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Old 08-01-2015, 12:04 PM
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The truck measures the fuel used through a transducer in the fuel line. You may just have a faulty, or mis-calibrated fuel transducer. Judging by everything else, it's probably a setting that a mechanic can access to correct the fuel measurement.
 
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Old 08-01-2015, 12:05 PM
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I don't have as many miles yet, but mine has been both high and low by less than 1 MPG so far.
 
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Old 08-01-2015, 12:48 PM
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I could understand plus and minus swings as that could be due to over or under filling the tank. But, to always be optimistic, and seemingly getting worse, when others say theirs is close, worries me. Maybe it can be calibrated as you suggested.
 
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Old 08-01-2015, 05:28 PM
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Originally Posted by Gary Lewis View Post
Tim - I agree that the MPG we get is subjective, but not the variance between actual and indicated MPG when measured over consecutive tanks. If I over or underfill on one tank it will show up on the next as noticeably better actual MPG than indicated MPG. But in my case the difference between actual and indicated is getting worse.

You may notice that I haven't complained about my actual MPG in this thread. While I'm not pleased with it, I'm trying to keep this thread to a discussion of the difference between actual and indicated. But, as said in the first post, "…if you aren't capturing the info for consecutive tanks then it may not be accurate since it is quite possible to overfill the tank one time and underfill it the next and heavily skew the MPG."

When you say "Mine has been very consistent as well", does that mean you have tracked your actual per-tank MPG over several tanks and find that it tracks closely with the indicated MPG? I'd really like to see what others have recorded so I can compare it to mine, and am quite willing to put the info in a spreadsheet for you/them if you'd like so we can compare apples to apples.
I've always gone by the lie o meter since I measured actual back when the truck was new. It was so close that I stopped tracking or comparing the two. The lie o meter has remained consistent and has never left me with a reason to doubt actual fuel consumption.

I drive 32 miles daily back and forth to work and I rarely drive anywhere else during the week. So on Sundays when I gas up I pump very close to the same volume each week.
 
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Old 08-01-2015, 05:59 PM
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I'm glad the LoM works for some of you as that suggests there's hope for mine. Hope so.
 
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Old 08-01-2015, 08:51 PM
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On my previous 2011 F350, gallons used was consistently 3 - 3.1% off which for my 65 gallon tank was right around 2 gallons. Always in the direction of it said I used less gallons than actual. On that truck for the most part I used the same fuel station and same pump and let it go until it clicked itself off. The LOM was off and there is no question about it. Still it is a very useful tool and once you know how far off you are, you will always know how much fuel you have if you reset one of the trip meters when you fill up.

So far on my 2015 F150, I've only filled up once after initially topping up whatever the dealer gave me. It was 3.56% off. Again, it said I used less than I did. For a 36 gallon tank that will come to a little over 1 gallon. Going by my previous experience, I'm expecting to see that 1 gal difference every time.

I expect the thing to be off because it has been optimistic on every vehicle I have owned which computes this stuff and not just Fords. But I expect it to be more or less the same percentage off each time. In your case the difference between your 4% and 8% would be over 1 gallon. I'd try doing the next several fills at the same station, same pump, and pointing truck in the same direction and letting it go until it stops by itself and see what happens.
 
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Old 08-01-2015, 09:23 PM
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Alex - Thanks. I think I'd be ok if the error was a given percentage of the fuel used, like yours was. But, as you point out, on mine there's a trend in the wrong direction.

However, you got me thinking about the amount of fuel used vs the error, so I laid in a few more calc's. The yellow cells are calculated fuel usage off the LoM's indicated MPG. And the column on the far right is then the error, in gallons, with the LoM always being low on usage. But, as you point out, it is getting worse with each tank. And, it isn't a function of the miles driven as each of the successive tanks has been over slightly fewer miles. So, I'm stumped as to why it is wrong, and really confused as to why the error is getting worse.

 
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Old 08-01-2015, 10:09 PM
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Yes, I saw your trend line and I'd be wondering about that myself.

I also saw your other post about mileage as well.

Over 400 miles I did on the first fill I got 21.2 mpg hand calculated with driving conditions similar to what you described.

Have you ruled out a fuel leak?
 
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Old 08-01-2015, 10:13 PM
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I have a 2010 with the 5.4 and the indicated mileage is anywhere from one to two mile/gal higher than what I calculate. It has been that way since I bought it, nearly 100,000 miles ago.
I also have a 2011 with a 5.0 and it is never more then .2 off but always more optimistic.
 
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Old 08-02-2015, 02:27 AM
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Gary: About a year ago, the dealer reprogrammed the computer on my (now former) 2013 Escape 2.0T because the MPG FoMoCo was claiming for the Escape and C-Max Hybrid was off, according to the US Gov't, by as much as 20%.

I'll keep you informed inre to the LoM of my new 'wearing Blue Jeans' Stupor Crew that I acquired about 8 hours ago (PDT).
 
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