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09-20-2018, 02:10 PM
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#1
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Senior Member
Name: Bob Ruggles
Trailer: 2015 Escape
Michigan
Posts: 1,537
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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. I’d like to believe the computer but I’m a chicken and don’t want to hand calculate for fear that I’ll be disappointed.
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09-20-2018, 02:29 PM
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#2
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Senior Member
Name: David
Trailer: 2013 Scamp 13 S1 BB
IL
Posts: 281
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Quote:
Originally Posted by rgrugg
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. I’d like to believe the computer but I’m a chicken and don’t want to hand calculate for fear that I’ll be disappointed.
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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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09-20-2018, 04:16 PM
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#3
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Senior Member
Name: John
Trailer: Roamer 1
Smith Valley, Nevada
Posts: 2,879
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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?
__________________
I only exaggerate enough to compensate for being taken with a grain of salt.
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09-20-2018, 04:24 PM
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#4
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Senior Member
Name: Steve
Trailer: Escape 15A
Minnesota
Posts: 452
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Stressing about mpg is bad for your health.
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09-20-2018, 04:30 PM
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#5
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Senior Member
Name: Bob Ruggles
Trailer: 2015 Escape
Michigan
Posts: 1,537
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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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09-20-2018, 04:32 PM
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#6
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Senior Member
Name: Bob Ruggles
Trailer: 2015 Escape
Michigan
Posts: 1,537
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I don’t stress about it. Whatever the truck gets it’s 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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09-20-2018, 04:34 PM
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#7
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Senior Member
Name: Jon
Trailer: 2008 Scamp 13 S1
Arizona
Posts: 11,912
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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. [emoji6]
Have I mentioned I like your signature line, Raspy?
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09-20-2018, 09:48 PM
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#8
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Senior Member
Name: Mike
Trailer: 2012 Escape 19
Oklahoma
Posts: 6,018
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They don't call it a lie-o-meter for nothing.
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09-21-2018, 07:29 AM
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#9
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Senior Member
Name: John
Trailer: Roamer 1
Smith Valley, Nevada
Posts: 2,879
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Quote:
Originally Posted by Jon in AZ
Have I mentioned I like your signature line, Raspy?
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Thanks. Yep, exaggerating in the interest of truth.
__________________
I only exaggerate enough to compensate for being taken with a grain of salt.
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09-21-2018, 07:13 PM
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#10
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Senior Member
Name: Steve
Trailer: Scamp 13
California
Posts: 1,890
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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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09-21-2018, 08:23 PM
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#11
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Senior Member
Name: John
Trailer: Escape 21, behind an '02 F250 7.3 diesel tug
Mid Left Coast
Posts: 2,937
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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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09-22-2018, 05:35 AM
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#12
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Senior Member
Name: Gordon
Trailer: 2015 Scamp (16 Std Layout 4) with '15 Toyota Sienna LE Tug
North Carolina
Posts: 5,155
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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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09-22-2018, 05:51 AM
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#13
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Junior Member
Name: Carl
Trailer: Scamp 16
Pennsylvania
Posts: 4
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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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09-22-2018, 06:57 AM
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#14
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Senior Member
Name: Jon
Trailer: 2008 Scamp 13 S1
Arizona
Posts: 11,912
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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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09-22-2018, 07:42 AM
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#15
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Senior Member
Name: Bob Ruggles
Trailer: 2015 Escape
Michigan
Posts: 1,537
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When I hear towing fuel mileage claims most of the time I don’t believe it. I have towing experience going all the way back to 1962 and have towed just about every kind of rv trailer so have a pretty solid idea of what mpg is reasonable.
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09-22-2018, 10:12 AM
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#16
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Senior Member
Trailer: Escape 17 ft
Posts: 8,317
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Quote:
Originally Posted by gordon2
All my Toyotas have had a speedometer that read high, and that is very common.
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How do you know this?
__________________
What happens to the hole when the cheese is gone?
- Bertolt Brecht
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09-22-2018, 10:12 AM
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#17
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Member
Name: William
Trailer: 13' Perris Pacer
California
Posts: 46
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Only one way to find out the computer's accuracy: FIND OUT! Fill the tank, record the odometer reading, drive, refill the tank, and calculate the MPG. My 1989 Lincoln Continental was always spot-on. My current 2004 Mercury Sable is always 2-3 MPG optimistic. I guess the technology was better back in the 80's.
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09-22-2018, 10:44 AM
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#18
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Senior Member
Name: Francois
Trailer: Bigfoot
British Columbia
Posts: 1,163
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Life...
Life's too short to spend time worrying about MPGs.... while towing my hotel suite on wheels (with kitchen!) from place to place ...whatever it costs...it costs.
I could always "go back in time" and travel by motorcycle with a pup tent strapped on the back of it... stellar MPG numbers there.....but that ain't happening!
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09-22-2018, 11:00 AM
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#19
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Senior Member
Name: alan
Trailer: looking
Colorado
Posts: 264
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When I was a kid we’d calibrate the odometer using mileposts and assume that the speedometer error correlated. GPSs ended that.
The lie-o-meter on my ‘11 F-250 (anecdotally, I never recorded the numbers) was from .3 to .7 MPG optimistic.
My F-250 died a terrible death (with me in it) in a hailstorm. The lie-o-meter on my ‘17 F-350 that replaced it, based on only three fuel refills, is about .2 to .3 MPG optimistic. On both trucks I assumed that the odometer is correct since the speedometers seemed to have only minor errors.
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09-22-2018, 11:08 AM
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#20
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Senior Member
Name: Steve
Trailer: 2018, 21ft escape— 2019 Ram 1500 Laramie
NW Wisconsin
Posts: 4,500
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I use my onboard computer to occasionally check my MPG’s more out of curiosity than anything else. I never expected great fuel mileage when towing and have never been disappointed
When we are going on a trip , I am more concerned about getting there safely and comfortably then fuel mileage
If fuel mileage was my major concern then I would probably sell my trailer and stay home .
My vehicle speedometer matches my GPS speedometer exactly . Since I drive the speed limit and seldom faster than 62 MPH , that’s close enough for me
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