Calculated AVG MPG Accurate??? -
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post #1 of 6 Old 10-09-2019, 05:30 PM Thread Starter
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Calculated AVG MPG Accurate???

2011 Overland 5.7L... my question is has everyone found the trip computer calculated AVG MPG to be accurate??? Iím hovering a hair under 18mpg AVG. That strikes me as optimistic compared to what I recall the 5.7L is rated at AVG MPG, something like 13/18 AVG if memory serves.


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post #2 of 6 Old 10-09-2019, 09:15 PM
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No. I write my calculated MPG on every gas receipt and compare it to the dash. Although I don’t have your model year as a direct comparison, I find my ‘16 dashboard display MPG always reports higher numbers than my hand calculated amounts by 5% or so.

The rare exceptions are when I take long uninterrupted road trips on the highway. Then the 2 numbers match up pretty closely.

I have found the mismatch to be present with every car I have owned that had a fuel economy calculator (Jeeps, Fords, Toyota, BMW, Audi, MB). The computer measures estimated fuel use. It doesn’t know exactly how many ml flowed through the fuel injectors. It guesses conservatively, leading to a higher figure.

Some manufacturers (Audi) have a correction factor setting you can program to calibrate it (sort of). But it still uses an estimate.

You know exactly how much gas you pumped back into the tank to fill it to the top, and exactly how many miles you drove since the last fill up. (Because you reset the tripometer ). Miles/gallons.
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post #3 of 6 Old 10-10-2019, 02:35 AM
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I have a 2018 HA 3.6. I always compare the computer estimates with my manual calculations. Although the computer tends to be on the optimistic side, it is usually within 0.5 mpg of my calculated result.
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post #4 of 6 Old 10-10-2019, 07:49 AM
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I think mine is accurate.

Check trip odo with mile signs on the highway. Similar distances?

Or use GPS.
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post #5 of 6 Old 10-10-2019, 08:24 AM
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Mine on all three of my vehicles are always about 1-2 mpg optimistic. Old fashioned hand calculations are always a little lower.

2014 Deep Cherry Red GC 4X4 V8 QDII
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post #6 of 6 Old 10-10-2019, 08:03 PM
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I generally show 1mpg higher on panel average, so that would match-up pretty well with 9496ZJs comment about a 5% difference. This can be of great value if you are the sort that runs the fuel tank to fumes and relies on the miles remaining number.
I had a Buick Regal with the mpg calc and that showed to be generous by 1mpg.

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