MPG Computer Accuracy

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HawkX66

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Shutterbug57, I drive a '15 limited with about 42k miles and ever since it was new the computer mpg has consistently been approx 1.4 to 1.6 mpg higher than when I hand calculate it.
I too don't understand why this is, or how they calculate mpg. Must use some kind of "new" math other than how many miles traveled divided by how many gallons it took to drive those miles.
For 3,000 miles mine has shown exactly the same. It doesn't matter if I drive highway from fill up or it's stop and go. The end result is close to the same variance.
Keeping track of mpg is a good indicator of how well your truck is running or whether something needs attention.
 

TobyU

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How do you calculate it? Different people do it different ways and then many people claim they do it the most accurate way but I'm not quite certain about that. There's only one perfectly accurate way to do it and that wouldn't be good on your fuel pump.
 

HawkX66

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It's pretty straight forward. Fill up, drive X miles, fill up. Divide miles driven by gallons used. Repeat. Once you've done this a few times you can get a pretty accurate average.
 

Artie

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How do you calculate it? Different people do it different ways and then many people claim they do it the most accurate way but I'm not quite certain about that. There's only one perfectly accurate way to do it and that wouldn't be good on your fuel pump.
I use the ‘car minder’ and ‘AUTOsist’ apps for iOS to track mine.
 

TobyU

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It's pretty straight forward. Fill up, drive X miles, fill up. Divide miles driven by gallons used. Repeat. Once you've done this a few times you can get a pretty accurate average.
Yes and the key term is pretty accurate. So if people are saying that their in car mpg reading is 1 mile per gallon higher or something there is still room for error in people's testing procedure when they do it manually.
There's no real way to know that you're feeling it the same every time unless you're crazy like I did a few times on one of my Town Cars and filled it till it was literally coming out of the neck of the car but that takes a long time.
That's a little more accurate though. To be extremely accurate you would have to do like MythBusters does and have external fuel tank for you had a set amount you can measure exactly. Or the heart of the fuel pump weigh as I mentioned. You'd have to run the car until it ran out of fuel. Put exactly 5 gallons in and then drive it again until it ran out of fuel again and you know exactly how far you went on 5 gallons.
 

HawkX66

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We're not talking about accuracy for the space shuttle. Most of us are just trying to get a "pretty accurate" measurement. If you fill it the same way each time, air space in the tank anomalies etc will become less and less of a factor. That's why you take the average of all the averages ignoring any outliers.
 

aggiegrad05

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We're not talking about accuracy for the space shuttle. Most of us are just trying to get a "pretty accurate" measurement. If you fill it the same way each time, air space in the tank anomalies etc will become less and less of a factor. That's why you take the average of all the averages ignoring any outliers.
Yep. Yes, unless you fill up at the same actual pump at the same time of day every time there will be anomalies, but if you do it using the "fill up-drive-fill up-divide miles by the number of gallons" method many multiple times and the computer is always high, that will scrub out most of the anomalies and tell you that the computer is high.

Another good equalizer is the lifetime average. The day I bought the vehicle I reset Trip 2 to 0 and have never touched it. So that shows what my truck believes to be it's lifetime average MPG...and it's 1.4 mpg higher than the combined average of all my hand-calculated fill ups.
 

TobyU

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Yep. Yes, unless you fill up at the same actual pump at the same time of day every time there will be anomalies, but if you do it using the "fill up-drive-fill up-divide miles by the number of gallons" method many multiple times and the computer is always high, that will scrub out most of the anomalies and tell you that the computer is high.

Another good equalizer is the lifetime average. The day I bought the vehicle I reset Trip 2 to 0 and have never touched it. So that shows what my truck believes to be it's lifetime average MPG...and it's 1.4 mpg higher than the combined average of all my hand-calculated fill ups.
I just don't worry too much about it being a mile per gallon higher. Maybe they just do it to make us feel better. I'm okay with that. I like to feel better more than I like accuracy. But don't get around any engineers. They will lose their minds. Then they will take stuff apart especially lawn mowers and damage them and cause more problems for the tech to fix them. Like the two this month that took their Muffler off to fix what they thought was a fuel delivery issue. One even thought it was the carburetor!
I just know the mpg meter is quite accurate. The harder I drive and the more I idle, the lower it goes.
 

TobyU

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Wow, just wow....

Why in the world does that wow you?
As long as every Ford product or every car has the numbers slightly higher then we can still all compare them. Since we're in an expedition forum we can assume that all the Expeditions for a relative number of years are all going to be the same amount of an accuracy so we can compare what we get to what others get.

Does it wow you that I could care less if my auto MPG indicator is less than 10% off? Or does it bother you more that they are?
I have just basically always use one as a relative up or down for how my car is running or in current conditions. I've never really cared about the exact number is. When the tank gets low I have to put more gas in whether I was getting 12 miles to the gallon or 25 miles to the gallon.
 

HawkX66

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You made the statement so I'm not surprised you don't get what's wrong with it. Nothing to do with the accuracy of the lieometer or how important or not important someone thinks it is.
 

cmiles97

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How accurate is the odometer? Shouldn't we use GPS or cell phone for mileage tracking? How accurate are GPS or cell phones?

What if I fill up on a 90F humid sunny day vs a completely different gas station at 50F and dry outside? How accurate are the meters on the pumps?

I'm fine with 1 mpg difference. My 17 is still doing 4mpg better than my 07 sequoia, relatively speaking.
 

TobyU

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You made the statement so I'm not surprised you don't get what's wrong with it. Nothing to do with the accuracy of the lieometer or how important or not important someone thinks it is.
Well thanks for explaining that!
Are you an engineer?? I can see many or most of them being perturbed because it not being accurate. They probably don't care whether it's off to the high or low side. It bothers in the same either way. I would much rather it be off to the high side and make me feel like I'm getting better mileage than off the low side but I think I already stated that.
Cmiles97 seems to share my fairly nonchalant attitude of mile per gallon indicator accuracy.
I know I'm an opinionated bastard but this wasn't even a major hang up or disagreement of mine.
Still makes no sense why you would be so surprised that someone wouldn't care about the accuracy being 1.4 off or why I would prefer to have it high as others seem to be fairly complacent about it also.
 
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Shutterbug57

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I just don't worry too much about it being a mile per gallon higher. Maybe they just do it to make us feel better. I'm okay with that. I like to feel better more than I like accuracy.

Ford has a history of ignoring facts. Admittedly, the MPG calculator is a minor annoyance, not even an issue in reality and that is the immediate context for your comment. I am curious, however, how far the laissez faire approach goes.

Would it extend to Ford saying (despite knowing to the contrary) Pinto gas tanks are safe (implied by selling the car with a known safety defect)?

If not that far, how about Ford saying the Fiesta/Focus transmission is reliable - again, despite knowing better?

If not that far, where (to you), between major safety/reliability issues and minor annoyances like MPG computers do facts matter over feelings and what causes the flip in priority? I am truly curious. Being a CPA (i,e., the facts matter crowd), I expect engineers to be able to do something simple like calibrate a flow meter to show accurate MPG. Unlike the Pinto, Fiesta & Focus issues, getting the MPG right has very little incremental cost and could probably be corrected with an automatic flash update downloaded while parked in your garage.

FWIW - I find it amazing that Ford can engineer a big old hulking truck that gets 20+/- MPG and not be able to accurately calibrate a flow meter. Is that a show stopper, no it’s not, not even close.
 

TobyU

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Ford has a history of ignoring facts. Admittedly, the MPG calculator is a minor annoyance, not even an issue in reality and that is the immediate context for your comment. I am curious, however, how far the laissez faire approach goes.



Would it extend to Ford saying (despite knowing to the contrary) Pinto gas tanks are safe (implied by selling the car with a known safety defect)?

If not that far, how about Ford saying the Fiesta/Focus transmission is reliable - again, despite knowing better?

If not that far, where (to you), between major safety/reliability issues and minor annoyances like MPG computers do facts matter over feelings and what causes the flip in priority? I am truly curious. Being a CPA (i,e., the facts matter crowd), I expect engineers to be able to do something simple like calibrate a flow meter to show accurate MPG. Unlike the Pinto, Fiesta & Focus issues, getting the MPG right has very little incremental cost and could probably be corrected with an automatic flash update downloaded while parked in your garage.

FWIW - I find it amazing that Ford can engineer a big old hulking truck that gets 20+/- MPG and not be able to accurately calibrate a flow meter. Is that a show stopper, no it’s not, not even close.

That would be an interesting discussion I guess. I'm just not very nitpicky about many things in life. Also not about punctuality. I can't stand for anyone to be early. If I tell someone to be at my place at 2:15 and they show up at 2:10 or 2:11 it ****** me off beyond belief. 215 means to 15 or within 10 minutes. I consider anything within 10 minutes after to be on time. I am weird. I always give a 10 minute late grace period But never an early one.

The exception is if you are coming in to relieve someone from a shift at work and you are holding them up but not being there early or on time. I used to have a job where we came in at 5 or on the weekends came in at 2. I expect you to be there walking up and taking over for that person at 2 p.m. sharp so they can leave their post. Even if you are one minute late you're making them wait on you and they want to go home.
It irritates me to no end when managers and companies have a big deal about tardiness when there's multiple people there and there's no rush for employees to be there to do the work. Used to have a morning job where we were there a full hour before the store opened. We were printing up the daily papers for all the customers we had to call hassle about making their payments, a rent-to-own store. More evil than the devil.
We had plenty of downtime there and the managers all sat around and drink coffee and smoke cigarettes anyways. But they act like it was the end of the world if you got there 12 minutes after 9.
I also eventually snarkily told one that they waste the same 12 minutes or more drinking and making coffee but they were getting paid for it. Most companies after 7 minutes will dock you for a full 15 which is totally fine. I only expect to get paid for the time that I'm working and if you only pay in 15 minute increments that makes sense. But when there is no pressing matter for an employee to be there there's no reason for them have to clock in at 9 Sharp. 9:05, 9:07, 9:12 is totally fine in my book.
I have been a manager over a crew of Warehouse employees also. You just have to get to know your managers. You know what they like and don't like. My people knew I had no problem as long as they were there when they were needed. They knew what I wouldn't tolerate and that's theft. When somebody stole something and then we needed it later to fix something or for a customer we were highly inconvenienced. It wasn't about the money or the company. If you're going to steal one make sure they order two. Do not leave me without one in stock when I need it.
In the early days of MPG meters they were vacuum gauges that just showed you when you were using a lot of fuel or less fuel. That would be easy to calibrate and there could simply be a little adjustment screw on the back of the current meters to literally adjust them up or down one mile per gallon. And on the more electronic ones they can incorporate it into the system. I have had a digital thermostat in my house for 15 years that allows you to adjust the temperature it shows because you may not like it showing that temperature or it may actually be inaccurate. So if you are convinced your house is 72° but the thermostat says 73 you can make it say 72 when you think it's 72. This would be just a simple on the in car information center.

Since you brought up the pinto I will have to say my joke that we did for years in the 80s. The Mustang II was just a pinto with the bolt sawed-off.

I hate it when manufacturers don't step up to the plate or go back and fix annoying common problems and failures that can easily be fixed. I know it's about money to them and if they would have started putting a shorter Bolt during the run that would have been admitting there was a problem with the earlier ones so therefore the lawsuit would have come in even quicker and made them more liable.

I just don't have an issue with the mile per gallon meter being up to 2 miles per gallon off. What I do have an issue with is the distance to empty. But those are fine. I haven't had a car yet that would run out as soon as it hits zero. If I fill up my car and it tells me I can go 300 miles, and I go on a trip that I know is 250, I do not want to have to stop and get gas before I get there. And I also want it to tell me I have 8 miles to go and I can get those eight miles without running out of fuel.

And as I stated from beginning if we have to have a 1 mile per gallon discrepancy I would much rather the gauge show 21 miles per gallon as opposed to 20.
It would be nice if the margin of error was 5 mile per gallon or less.

The older I get the more I love the expression... Close enough for government work.
 
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Shutterbug57

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Well, I put my third recorded fill in the truck. My deltas have been +1.4, +1.2 & +1.3, so it looks like that is the ballpark for this truck’s delta - similar to that of others. Now I have a better idea of how to read the trucks posted numbers.
 

TobyU

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Well, I put my third recorded fill in the truck. My deltas have been +1.4, +1.2 & +1.3, so it looks like that is the ballpark for this truck’s delta - similar to that of others. Now I have a better idea of how to read the trucks posted numbers.

Yep. If the number goes up, your getting better mileage, going downhill, or being towed.
If it goes down, you're driving it harder, idling too much, got lousy gas in it, or engine not performing like it was.

On the topic of gas and mileage.
Everyone who talks about it says they get better(usually 1-3) MPG with not ethanol fuel.
Some claim ridiculous gains...

If you can get non-ethanol conveniently and for no more than $.20 or so more per gallon, you might try that and compare it to 10% ethanol. Makes life interesting, and like the high reading gauges, it pure gas makes my number go up....MAKES me feel better.
All warm and fuzzy actually. That and a couple of warm fresh brownies and a huge glass of milk....and I'm a happy bastard. For a while.....
 

TobyU

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Put one foot in front of the other..... It's the snowbominable monster snowmonster thingy.
 
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