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Thread: Trip Computer MPG

  1. #16
    Registered Member Kaps's Avatar
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    Quote Originally Posted by shadonoz View Post
    How do you know that? Can you tell us more about this method or where to learn more about it? I'm trying to imagine how it would work without measuring the fuel.
    I don't know the specifics - it could use some sensors to verify how long the throttle position is depressed and how quickly it is depressed to calculate approx. fuel consumption and match it against distance but I don't think any car measures the volume of fuel used and takes that into calculation. That is true for all makes and models. So this is again a guesstimate and it depends on driving / commute etc. There are circumstances where it overestimates fuel used and others where it does not.

    Main point is Mazda or any other maker is not trying to fool anyone by showing higher than actual mpg on the dash. It is a calculation and is not accurate in all conditions.

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  2. #17
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    I have no reason to monitor the miles per gallon (or kilometers per liter which is what my car reports) because I climb a 14 kilometer mountain road almost every day and know full well my milage is going to be lousy. What most interests me is the reported range I have left since I am sometimes in areas without gas stations.

  3. #18
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    Quote Originally Posted by Avoidin Deer View Post
    Any variances between the computer and manual calculations even out the next tank or two of gas.

    It only takes a little under-filling the tank when you start off to make it look like your mileage declined (because it took that much more gas to fill up at the end of that tank). Conversely, if you under-fill some at the end of the tank, it looks like your mileage is higher than the computer stated because it seems you went through a lower amount of fuel.
    What you said would be true if the trip computer were accurately estimating MPG.
    And this is why I know mine is NOT accurately doing so...

    For ALL of my 50+ fill-ups, the trip computer has shown higher than actual MPG. It NEVER evens out.
    I can stop pumping at the first click, or fill it to the brim after 3-4 clicks.
    The trip computer will always show an artificially high MPG.

  4. #19
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    Quote Originally Posted by Avoidin Deer View Post
    I've been keeping mine in a spreadsheet every time I fill up so I can track mileage by octane & brand. I have about 4,400 miles on my car and am on my 17th tank of gas.

    Any variances between the computer and manual calculations even out the next tank or two of gas.

    It only takes a little under-filling the tank when you start off to make it look like your mileage declined (because it took that much more gas to fill up at the end of that tank). Conversely, if you under-fill some at the end of the tank, it looks like your mileage is higher than the computer stated because it seems you went through a lower amount of fuel.

    It's not hard to do. Not all gas stations are perfectly level.

    But (surprisingly) the computer is accurate.
    Yes, but that under-filled tank will have yielded a higher calculated mileage for the previous driving. It should work itself out if you do it each time. If this were the source of the discrepancy, the Mazda should compute better mileage sometimes, and worse others. Mine consistently reports better from the computer than odometer change/fill volume.

  5. #20
    Structural Member shadonoz's Avatar
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    Quote Originally Posted by Avoidin Deer View Post
    I've been keeping mine in a spreadsheet every time I fill up so I can track mileage by octane & brand. I have about 4,400 miles on my car and am on my 17th tank of gas.

    Any variances between the computer and manual calculations even out the next tank or two of gas.

    It only takes a little under-filling the tank when you start off to make it look like your mileage declined (because it took that much more gas to fill up at the end of that tank). Conversely, if you under-fill some at the end of the tank, it looks like your mileage is higher than the computer stated because it seems you went through a lower amount of fuel.

    It's not hard to do. Not all gas stations are perfectly level.

    But (surprisingly) the computer is accurate.
    Quote Originally Posted by murky View Post
    Yes, but that under-filled tank will have yielded a higher calculated mileage for the previous driving. It should work itself out if you do it each time. If this were the source of the discrepancy, the Mazda should compute better mileage sometimes, and worse others. Mine consistently reports better from the computer than odometer change/fill volume.
    Quote Originally Posted by bluegrass View Post
    What you said would be true if the trip computer were accurately estimating MPG.
    And this is why I know mine is NOT accurately doing so...

    For ALL of my 50+ fill-ups, the trip computer has shown higher than actual MPG. It NEVER evens out.
    I can stop pumping at the first click, or fill it to the brim after 3-4 clicks.
    The trip computer will always show an artificially high MPG.
    Well that settles it then, doesn't it.
    Avoiding Deer's works the way it's theoretically supposed to. And he's verified it.
    Murky's and bluegrass' don't work that way, and they've verified it.
    That's life!

  6. #21
    Registered Member Conrad 16.5's Avatar

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    Quote Originally Posted by 7eregrine View Post
    A lot of people calculate manually because it is so ridiculously easy nowadays.
    This app:
    https://play.google.com/store/apps/d...m.kajda.fuelio

    has been installed over million times. And there are many others.
    And here's one for the Apple heads:
    https://apps.apple.com/us/app/fuelly...er/id295905460



    1995 called bro and wants you to get an app. Some of them synch to your PC or let you download it all if you want. Notebooks?!?
    I called 'em back and told them to forget the app. I also told 1995 that I'll bet a LOT of people these days don't even know how to divide the number of miles driven by the number of gallons used to calculate their fuel economy.

    Don't you fret though, I'm no luddite. I'm no stranger to tech and I use lots of apps for other things, just not tracking my fuel economy.
    "Don't bother me with facts, Son. I've already made up my mind." -Foghorn Leghorn

  7. #22
    Registered Member 7eregrine's Avatar

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    Quote Originally Posted by Conrad 16.5 View Post
    I called 'em back and told them to forget the app.


    I also told 1995 that I'll bet a LOT of people these days don't even know how to divide the number of miles driven by the number of gallons used to calculate their fuel economy.
    Yea, but it's easy to figure it out, so I bet it's more common then you think: "Hey Google. How do I calculate MPG?" lol

  8. #23
    Registered Member Conrad 16.5's Avatar

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    Quote Originally Posted by 7eregrine View Post



    Yea, but it's easy to figure it out, so I bet it's more common then you think: "Hey Google. How do I calculate MPG?" lol
    That's very true, ask Google. I'd ask Alexa though, if I didn't know how.

    My point is that, in my opinion, not many could figure it out themselves. Let's see miles PER gallon, miles/gallon. How do I calculate that!
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  9. #24
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    For those manually logging & computing your MPG, are you doing it per tankful or computing a longer-term average? I feel you need to average it over a longer period of time for accuracy. And I'd guess (but haven't looked it up) the Mazda computer keeps a running average until it is manually reset.

    Regardless, you can't compare the two numbers unless you use the same methodology.

    But what I really want to know is how many of you have run until the tank is empty just to see how accurate the trip computer's "miles-remaining" calculation is.

    That's what I look at on a long trip.
    Last edited by St1ngy; 10-09-2019 at 10:13 AM.

  10. #25
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    I calculate it and keep a record in Fuelly. My CX-5 was always equal to the computer when calculated over 2 tanks. My CX-9 computer is always 0.4-0.6 MPG higher than the calculated.
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  11. #26
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    you're kidding right! You get upset that the computer is off a couple of miles per gallon? Put a piece of electrical tape over the display and forget about it. They provide you with something like this and you get upset? What would you do if you didn't have power windows, air conditioning, or power seats. This thing gets better mileage than my 1966 40HP VW bug that I had to push start until I fixed the starter. Be Happy!!!!!!!!!!!!!!

  12. #27
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    Quote Originally Posted by St1ngy View Post
    For those manually logging & computing your MPG, are you doing it per tankful or computing a longer-term average? I feel you need to average it over a longer period of time for accuracy. And I'd guess (but haven't looked it up) the Mazda computer keeps a running average until it is manually reset.

    Regardless, you can't compare the two numbers unless you use the same methodology.

    But what I really want to know is how many of you have run until the tank is empty just to see how accurate the trip computer's "miles-remaining" calculation is.

    That's what I look at on a long trip.
    I do it per tankful, and keep a running record of it:


    Here are the fields:
    Date: Date I filled up
    Station: Brand/Location purchased of the just-consumed tank
    Octane: Octane of the just-consumed (93 is highlighted)
    Miles: Miles driven on the just-consumed tank (Trip A, gets reset every tank)
    #Gals: Number of gallons at this fill up
    Calc: Manual MPG calculation of the just-consumed tank
    Comp: Computer's MPG of the just-consumed tank (Trip A, gets reset every tank)
    Calc vs Comp: Calculated MPG vs Computer MPG, in actual MPG and as a % of the Computer's MPG
    To Match Comp: #Gals/cups of gas more/less required for Calc MPG to equal Comp MPG for that fillup
    ---I did this so I could see how likely it is that large MPG differences were due to not topping off properly at the tank Start/End, and so I could track this to account for MPG differences from tank-to-tank.

    The first line is the tank the Dealer provided. It is not included in my calcs because I have no idea if it truly was a full tank.

    At the aggregate (about 4,400 miles), the Average Calculated MPG is .55 MPG higher than Average Computer MPG.

    Need I say it? YMMV
    Last edited by Avoidin Deer; 10-09-2019 at 09:03 PM.

  13. #28
    Registered Member 7eregrine's Avatar

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    Quote Originally Posted by shooter357 View Post
    you're kidding right! You get upset that the computer is off a couple of miles per gallon? Put a piece of electrical tape over the display and forget about it. They provide you with something like this and you get upset? What would you do if you didn't have power windows, air conditioning, or power seats. This thing gets better mileage than my 1966 40HP VW bug that I had to push start until I fixed the starter. Be Happy!!!!!!!!!!!!!!
    Ohhhh, I like this guy! And totally agree. Y'know the one thing I didn't give AF about when I bought my car? MPG.
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  14. #29
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    about 2k miles on my GTR. last fill up was 28.6 MPG,calculated manually. Mostly rural roads. Very pleased.

  15. #30
    Registered Member jonnymopar's Avatar

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    I bought mine last October and I had to check tank-to-tank because the trip computer was showing anywhere from 33.5mpg to 34.1mpg. I was highly skeptical that this bubble butt little SUV is getting that kind of gas mileage. I still can hardly believe it, but it actually is! Tracking by tank, it's always been within +/- 1mpg.


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