Gas mpg - Fiberglass RV


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Old 09-20-2018, 02:10 PM   #1
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Name: Bob Ruggles
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Gas mpg

Any opinions on how reliable the truck computer is in displaying mpg? On a 300 mile trip mine showed 23.4 mpg. I have a 2015 Ram 1500, 4x4, crew cab, 5.7 liter hemi with deactivation of 4 cylinders when conditions allow. I have a 3.21 axle. Iíd like to believe the computer but Iím a chicken and donít want to hand calculate for fear that Iíll be disappointed.
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Old 09-20-2018, 02:29 PM   #2
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Any opinions on how reliable the truck computer is in displaying mpg? On a 300 mile trip mine showed 23.4 mpg. I have a 2015 Ram 1500, 4x4, crew cab, 5.7 liter hemi with deactivation of 4 cylinders when conditions allow. I have a 3.21 axle. Iíd like to believe the computer but Iím a chicken and donít want to hand calculate for fear that Iíll be disappointed.
I have found, at least in Lexus vehicles, that the real time mpg is not spot on, but that the total mpg calculation over that of the whole tank is pretty much within a couple mpg of doing it with pen and paper. Towing a scamp 13 bunk version, 2 liter 4 cyl turbo, i averaged 19mpg on a 5,000 mile trip with lots of wind and mountains, hills in the mix.
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Old 09-20-2018, 04:16 PM   #3
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Better hand calc it.

That mileage number sounds very high for that truck and Rams are known for having "optimistic" mileage computers.

I'm sure you weren't towing, but were you going down wind the whole way with a speed of only 45 MPH, on level ground with the cruise control on?
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Old 09-20-2018, 04:24 PM   #4
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Stressing about mpg is bad for your health.
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Old 09-20-2018, 04:30 PM   #5
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Mostly level mostly 4 lane highway with cruise set at 60. Of the 300 miles probably only about 40-45 on two lane roads and no city driving.
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Old 09-20-2018, 04:32 PM   #6
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I donít stress about it. Whatever the truck gets itís better than the previous Chevy Silverado 1500. The Ram had an 8 speed transmission while the Chevy had a six speed and the Chevy had a higher numerical axle.
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Old 09-20-2018, 04:34 PM   #7
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Gas mpg

Accuracy varies. Mine shows 1-2 mpg higher than I calculate manually.

When I first got the vehicle (my first with that feature) I tracked it manually for several months and compared the result with the on-board computer. Manual calculations can have variation, too, as not all gas pumps shut off at the same full mark.

If you want to know your fuel mileage to improve your driving habits or to be aware of a sudden, unexplained change that might indicate a mechanical problem, great (and it really doesn't matter if it's spot on or not). If you're looking for bragging rights, get over it. I never believe what anyone else says about their fuel mileage, anyway. It's in same category as age and weight.

Have I mentioned I like your signature line, Raspy?
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Old 09-20-2018, 09:48 PM   #8
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They don't call it a lie-o-meter for nothing.
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Old 09-21-2018, 07:29 AM   #9
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Have I mentioned I like your signature line, Raspy?
Thanks. Yep, exaggerating in the interest of truth.
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Old 09-21-2018, 07:13 PM   #10
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My 2016 Tacoma is very accurate based on tank mileage. That is what the display shows. Its not showing actual mileage at any given moment. However it caculates it, its doing a good job.
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Old 09-21-2018, 08:23 PM   #11
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even measuring your gas fills and dividing by mileage can vary by several MPG per tank as not all gas station pumps will fill the exact same level in your tank, so I ge tthe most accurate readings when I average several tanks..
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Old 09-22-2018, 05:35 AM   #12
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All my Toyotas have had a speedometer that read high, and that is very common. Better to err on the high side than the low side they figure. And they seem to show a correlated error in odometer and MPG reading. I pay no attention to the MPG readout. Using the "tank-fill" method yields pretty consistent numbers but there will always be some variation...

https://www.fueleconomy.gov/feg/why_differ.shtml
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Old 09-22-2018, 05:51 AM   #13
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Is it not better to use the cars odomerter. That way you have the average for towing and not towing. After all that is the real cost of a trip. My rav, reads 20.5 for towing and not towing over a length of time. Just my thoughts. Carl
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Old 09-22-2018, 06:57 AM   #14
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It comes down to motive. Why do you want to know?

If you want to compare one vehicle to another, you're better off using a source like Consumer Reports that uses a consistent testing methodology with calibrated instruments.

If you want to monitor changes over time, just watch the on-board computer. It doesn't matter if it's precise or not- you're looking for change. It wouldn't hurt to verify manually occasionally in case the computer is the problem. I agree that averaging several tanks is best when computing manually.

And if you want to make accurate statements in public discussions, use any method you want. There are far too many variables to make the conversation helpful. I suspect most people take fuel mileage claims with a grain of salt and a shrug.
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