Accuracy of MPG display in Dash

[yrraljguthrie]

I didn't see this posted. It likely has been and I missed it. I've only had my 2023 Bighorn for a couple of weeks and I don't yet have a handle on the accuracy of the fuel reading on the dash compared to real math. Can anyone give me a heads up on how close it is to actual?

 

[Mb7640]

I have a 21 warlock and mine is the same as doing the math. I get 16.5 mpg

 

[Tulecreeper]

I didn't see this posted. It likely has been and I missed it. I've only had my 2023 Bighorn for a couple of weeks and I don't yet have a handle on the accuracy of the fuel reading on the dash compared to real math. Can anyone give me a heads up on how close it is to actual?

I ignore it. Matter of fact, if I could figure a way to get it off my EVIC screen, I would do that. If I want to know my real MPG, I reset my trip meter to zero when I fill up then just do the math when I fill up again.

 

[huntergreen]

In my last 3 rams, the evic always .5 mpg over hand calculated.

 

[GTyankee]

The Lie-O-Meter exaggerates the MPG

If you actually care about your MPG, use a pencil & pad for 2 or 3 gas tanks of fuel

 

[turkeybird56]

The Lie-O-Meter may be close, kinda depends upon your truck. I have found mine to be between .5 to 1.5 mpg off, depending upon how driven and conditions. But overall, it is pretty close. Just remember, your gauge may not be calibrated to the size tank in your vehicle. But if you just do the math and hand calculate, U be good. Just remember to fill the tank the same way so your figures are pretty accurate.

ADDED: I did find on a trip on a highway at a consistent mph, using cruise as much as possible, was pretty dang close. Again conditions: truck tires, psi, temps, fuel type, load in vehicle, and and, too many variables.

 

[dhay13]

Depends on your riving conditions but I have an extensive spreadsheet with these numbers. Hold on a sec....

This is my 2018 Ram 2500 6.4. Sometimes actual is higher than the dash readout but usually actual is slightly lower

13.711​		evic read 14.2
12.897​		evic read 14.2
13.546​		evic read 14.6
13.507​		evic read 14.8
12.578​		evic read 14.1
12.370​		evic read 13.6
11.541​		evic read 13.2
16.813​		evic read 18.4
12.121​		evic read 13.4
11.211​		evic read 12.1
14.206​		evic read 15.5
11.018​		evic read 12.0
10.691​		evic read 11.4
14.687​		evic read 15.5
12.401​		evic read 13.5
11.931​		evic read 12.7
12.996​		evic read 13.9
13.760​		evic read 13.7
10.563​		evic read 11.1
13.139​		evic read 13.2
12.510​		evic read 12.5
13.466​		evic read 13.4
11.013​		evic read 11.7
10.865​		evic read 10.7
10.626​		evic read 11.3
13.274​		evic read 14.4
6.692​		evic read 7.4
11.271​		evic read 12.1
14.498​		evic read 14.5
12.374​		evic read 13.8
12.035​		evic read 12.3
12.428​		evic read 12.9
9.390​		evic read 10.4
13.558​		evic read 13.6
12.478​		evic read 13.3
13.447​		evic read 14.8
11.835​		evic read 12.7
10.880​		evic read 12.1
11.662​		evic read 13.6
13.327​		evic read 14.3
12.638​		evic read 14.1
11.183​		evic read 11.8
9.098​		evic read 10.3
12.838​		evic read 12.7
9.720​		evic read 10.3
11.764​		evic read 12.1
12.171​		evic read 11.9
9.945​		evic read 9.5
10.406​		evic read 11.3
12.569​		evic read 11.9
11.370​		evic read 12.0
10.943​		evic read 11.4
10.534​		evic read 11.2
9.974​		evic read 11.0
11.101​		evic read 12.1
11.441​		evic read 12.9
11.946​		evic read 12.9
11.631​		evic read 12.8
10.648​		evic read 11.4
10.375​		evic read 11.0
11.917​		evic read 12.4
10.621​		evic read 11.1
10.929​		evic read 10.9
10.460​		evic read 11.3
9.458​		evic read 9.3
11.378​		evic read 11.8
10.115​		evic read 10.2
10.521​		evic read 10.5
8.970​		evic read 9.7
11.165​		evic read 10.6
12.278​		evic read 12.4
9.539​		evic read 11.3
10.401​		evic read 11.0
10.105​		evic read 11.2
13.054​		evic read 13.8

 

[dhay13]

Here is a better screenshot

 

[dhay13]

yeah...I'm a nerd with too much time...lol

 

[REDinAZ]

my observation with the 5.7 is around town you'll see closer to 15, out on the interstate and set on cruise, you'll pretty much see a bit under or over 20.

 

[Dean2]

My 2021 2500 and our Jeep are both pretty close, usually within .5 mpg of hand calculated. However, I have had the displayed mileage be lower than actual on occasion, usually it reads a bit high, but not always. Have also had the Display mileage be out by a lot.

 

[BossHogg]

The Lie-O-Meter exaggerates the MPG

If you actually care about your MPG, use a pencil & pad for 2 or 3 gas tanks of fuel

You are assuming the DIC is wrong but your hand calculations are right (I'm sure your math is). How do you know that every time you fill up you are filling up to the exact same level as the times before? Do you factor in the temperature of the fuel with respect to expansion and contraction? A search tells us the coefficient of gasoline's expansion/contraction equals 0.069% per degree Fahrenheit. On a 15-gallon refill, that equates to just over one-tenth of a gallon per degree of Fahrenheit.

The DIC MPG is over time and is accurate from this facet, within reason. A +- one-tenth of a gallon difference between fill-ups will cause hand calculations to show an error of up to 0.4 (+-) miles per gallon. Make this an accumulative error over time in hand calculations and well, I'm sure you can see how the data becomes exaggerated.

I did a one-year comparison of DIC MPGs versus hand calculated. Sometimes my calculations showed higher MPG than the DIC and other times not. After one year, the delta between hand calculated and DIC was 0.837 MPG favoring hand calculations. While each instance showed a delta between hand-calculated and DIC, over time the delta was less.

 

[turkeybird56]

my observation with the 5.7 is around town you'll see closer to 15, out on the interstate and set on cruise, you'll pretty much see a bit under or over 20.

Yeah but soooo many factors: temp, tires, PSI,. rear end, 2 vs 4 WD, traffic, roadway, wind, loads in vehicle, fuel quality, truck MX, the lists are endless, lmao. and FTR, just IMHO, oh so very lowly and humble.

 

[Tulecreeper]

You are assuming the DIC is wrong but your hand calculations are right (I'm sure your math is). How do you know that every time you fill up you are filling up to the exact same level as the times before? Do you factor in the temperature of the fuel with respect to expansion and contraction? A search tells us the coefficient of gasoline's expansion/contraction equals 0.069% per degree Fahrenheit. On a 15-gallon refill, that equates to just over one-tenth of a gallon per degree of Fahrenheit.

The DIC MPG is over time and is accurate from this facet, within reason. A +- one-tenth of a gallon difference between fill-ups will cause hand calculations to show an error of up to 0.4 (+-) miles per gallon. Make this an accumulative error over time in hand calculations and well, I'm sure you can see how the data becomes exaggerated.

I did a one-year comparison of DIC MPGs versus hand calculated. Sometimes my calculations showed higher MPG than the DIC and other times not. After one year, the delta between hand calculated and DIC was 0.837 MPG favoring hand calculations. While each instance showed a delta between hand-calculated and DIC, over time the delta was less.

No one is looking for that detailed of a calculation...unless you're a Formula 1 driver.

 

[GTyankee]

LOL

Do your test in the Fall, when temperature fluctuations each day are minimal.

Fill up at 7 am each time, using the same gas station

Use the same driver, can't use a grand parent one time & a teenager the next.

The trips would have to be the same, highway driving & local driving would give you different results.

Screw it, i just barely passed arithmetic.

When my tank is down to a quarter of a tank, i start thinking about stopping at my usual gas station.

 

[Dean2]

Screen shot of my vehicle log, gas component for the 2021 Ram 2500 with 6.4 gas motor. As you can see I recorded the displayed MPG in the comments, versus the calculated MPG using gallons consumed for miles driven. Hand Calculation is not temp adjusted, but our pumps are regulated for output at a specific temperature, being 15 Celsius, and all fills are to the point the pump auto shuts off. The display is often close, most are over, but some under, but it can also be out a whole bunch too. Not sure what causes it to be closer some times than others.

 

[Tulecreeper]

Screen shot of my vehicle log, gas component for the 2021 Ram 2500 with 6.4 gas motor. As you can see I recorded the displayed MPG in the comments, versus the calculated MPG using gallons consumed for miles driven. Hand Calculation is not temp adjusted, but our pumps are regulated for output at a specific temperature, being 15 Celsius, and all fills are to the point the pump auto shuts off. The display is often close, most are over, but some under, but it can also be out a whole bunch too. Not sure what causes it to be closer some times than others.

View attachment 523843

Are you literally filling up every couple of days? I picked up my truck on March 24th, and I just filled up for the third time last Wednesday.

 

[Dean2]

Are you literally filling up every couple of days? I picked up my truck on March 24th, and I just filled up for the third time last Wednesday.

Depends on how much i am using it, obviously. I never leave town without having a full tank to start with. As you can see from the log, fills are anywhere from 4-700 klms and is normal between fills. I also don't let it get much below half before I fill given the opportunity. In my country there are very long stretches with no gas. I carry ten gallons in Jerry cans at all times when out of town. As you can also see, I filled once in May and once in June so wasn't driving it much those two months. Got the truck August 2021 and it still only has about 10,000 miles on it.

 

[IDSandman]

I only look at mine while coasting down hill or on the off ramp…

 

[Tulecreeper]

Depends on how much i am using it, obviously. I never leave town without having a full tank to start with. As you can see from the log, fills are anywhere from 4-700 klms and is normal between fills. I also don't let it get much below half before I fill given the opportunity. In my country there are very long stretches with no gas. I carry ten gallons in Jerry cans at all times when out of town. As you can also see, I filled once in May and once in June so wasn't driving it much those two months. Got the truck August 2021 and it still only has about 10,000 miles on it.

I'm sorry, I completely brain-farted the fact that I'm retired and put maybe 400 miles/650 kms on my truck each month. That does include, however, 200 miles back and forth to the lake(s) every month fishing. So, I drive 400 miles, fill up, then drive another 400 miles and fill up. But since I spread it out I only have to gas up every month.