Gas mileage computations are NOT accurate

[TarnishedCopper]

When the owner fills-up the vehicle and resets the economy calculator, drives 200+ miles, then fills-up again, why does the truck's computations say 17.4 mpg and my calculator say 16.76 mpg? I definitely trust my calculator much more than Ford's computer.

Sponsored

 

[Scotty_B]

I have been tracking my mileage since new with each tank, including a recent 1200 mile trip towing a 7,000lb trailer. My calculations are always slightly less than what is shown on the fuel mpg on the economy bar. I have noticed the economy bar varies greatly with throttle position and not necessarily actual fuel consumption. However, I have found that individual trip settings are pretty close to my calculation - even when towing.

It also seems like the fuel quantity gauge reads too low and may be compensating for a 5 gallon emergency reserve.

 

[Pedaldude]

Search Engineering Mode and you’ll find how to reset the MPG computer.

Don’t use the last tank for it but an average of a few tanks and wait for the break-in period to be over, or you’re probably going to have to do it again.

Good luck with your truck!

 

[UNIKRN150]

I've never put gas in my truck without filling the tank.

I always get a receipt and write the milage at the top of the receipt.

After 25k I have THICK STACK of receipts for every drop of gas I've put in my truck since I burned off the fumes it came with from Kansas City. (You'd think for what we pay they could at least fill the damn tank before delivery)

But... I've also never seen any reason to not accept that the computer's MPG is "close enough" to inspire me to actually pull out my receipts and start cyphering some actual fuel milage.

I save them in case I see some weird anomaly and need to go back and check.

Bottom line... It's a Full Size American 4x4 Pick Up Truck with a V8 engine.

I didn't buy it for the "great fuel economy"!

That'll be my NEXT truck!

 

[Buyer2021]

The perfect gif @Pedaldude ?

@TarnishedCopper - I hope you aren't too shocked by your 'discovery' and that you realize there's variables affecting the 'absolute accuracy' of both the 'display MPG' and your 'calculated MPG" (e.g. inconsistent fill-level in the case of the latter).

Just for grins at every fill-up I've been entering both values in my mileage spreadsheet for different vehicles for years and letting it compute the % difference. Excerpted from that spreadsheet here's the tabulation to date for my F150:

Actually, my F150 has less average disparity between the two than my previous Honda Ridgeline and Ford Escape with similar mileage display capabilities.

Not worth trying to adjust the F150's calculation for me, the only time I even look at it is when I fill-up, it doesn't have any bearing whatsoever on my driving behavior.

(You'd think for what we pay they could at least fill the damn tank before delivery)

Lol, should've bought from Granger Ford - mine was delivered with a FULL 36-gallon tank

 

[tbinmd]

Well don't forget that filling a tank at the pump is not exactly scientific. Only way to really check mileage is to use the same pump, only fill when the temp is the same. Even then you will have a variance. 4% isn't bad at all. Just like a torque wrench, nothing is exact.

 

[Gros Ventre]

The reality is you buy gasoline on a volume basis without any reference to density or temperature. Thus the actual amount of "energy" you purchase varies. Your engine responds to the actual energy injected into the cylinder. Thus the "gallons consumed" varies with temperature. The Ford computer responds only to volume, although Ford could program for energy content since they can measure fuel temperature... However MPG is so "culturally ingrained" in us that they wouldn't even try... A long time horse says to fill your tank early in the morning... When the gasoline is densist and you get more energy in each gallon.

 

[Zengineer]

When the owner fills-up the vehicle and resets the economy calculator, drives 200+ miles, then fills-up again, why does the truck's computations say 17.4 mpg and my calculator say 16.76 mpg? I definitely trust my calculator much more than Ford's computer.

Because it is harder to measure how much fuel was used without knowing how much it took to fill the tank. When you want two cups of water to make a cake do you pour it into a measuring cup or try to open the faucet exactly 38% open for 4.7 seconds?

And I assume you know by now you are the last person on the planet to realize the dashboard fuel economy number is not 100% accurate.1

 

[UGADawg96]

I've had eleven vehicles in the last 30+ years. I'm not sure with which vehicle they started displaying MPGs, but not one has been accurate on the dash. They have all generally been within 1-2 mpg of what the dash shows.

 

[jamnutz]

5 or 6% off is not bad at all, I've had vehicles that were over 15% off of actual hand calculated mileage.

 

[Jus Cruisin]

They've been nicknamed LOM (Lie-o-meter) for years. Nothing new.

 

[thebigdu]

I agree with others on here re. this truck being more accurate than past vehicles. I find if I don't use remote start heavily for a specific tank, the mpg reading is extremely close to my hand calcs. Remote start or extensive idling will increase the delta significantly.

 

[fordtruckman2003]

Gasoline expands with higher temperatures. The amount you put in tank will always vary because you are never going to be using same pump with same pressure cutoff switch with same fueling temperature. It's not like the old days when we didn't have totally sealed gas tanks to keep EPA happy. My 2003 truck I could get consistent fueling gallons against gauge reading. 1/4 tank was always x gallons, every time. My 2011 I kept 12 years and 1/4 tank on gauge would vary widely on the amount the gas pump would put into the tank. Even running down to totally empty I'd never be able to pump the listed tank capacity into it without pump kicking off.

So my 2¢ is that that gauge reading is likely more accurate than most assume it to be. Or at least it's an apples to apples comparison over time. There are too many variables with gas pumps to get consistent numbers you can rely on to accurately calculate MPG. Both methods will have a degree of error, but I rely on dash reading to tell me something is good or bad. I'll see the dash drop MPG when spark plugs start going bad before I will notice it on hand calculated numbers.

 

[TarnishedCopper]

Thanks for all the comments. With everything else being digital on the newer vehicles, it just seems the fuel gauge should be too. It computes out how many more miles one can travel on the fuel in the tank, so it must somehow meter the useage as well. When we buy it at the pump, they meter how much we get, why not a digital fuel guage? It would certainly be more accurate than an analog needle. Just a thought....I am still miffed at not being able to get the Nav package and Sirius/XM radio in my truck, as well as no CD player and no built-in programmable garage door opener.

 

[Jus Cruisin]

To the OP, don't get 'em wound up on "miles to empty".....

Sponsored