I have 2006 Big Horn SLT 5.9 ctd -48RE with 14k miles

I just did a MPG check doing this: Filled my tank all the way UUPP till I saw liquid [not first click or foam]. Then put about 250 miles on the truck going back forth to work [ 10 miles] and a few sixty mile trips on the freeway at 70 mph. Also includes just a couple minutes warm up in the morning while getting my jacket; lunch box etc.. Then refilled using same method above. Now with hard numbers off odometer I'm getting 14.496011 mpg BBBBUUUTTT the mpg up on the fuel analizer thingy from Dodge says I'm getting 16.5 mpg ?? Is this a scam issue and I use the term "scam" lightly; into thinking your getting reasonable fuel mileage from one of Dodge's big fat trucks and telling all of your none Dodge lovers how good your fuel mileage is compared to their fuel hogs; or I don't know how to use the fuel thingy?? Actual 14.5 mpg is far from 16.5 mpg when your braggin; if ya know what I mean---->

 

I get 14.5 with my mostly city driving also.

Scam? No. Some people's overhead error works the other way - the display is worse than actual.

 

My overhead ALWAYS reads 1.5 mpg better than what I actually net.

 

1.5 more seems to be normal.

 

Do you have the stock 265 tires?

I have 285r70s and I have to add 4% to my miles to get actual (checked with a GPS, odo to odo over a several hundred mile trip). That helps reconcile the overhead and actual a little better, still off by about 10% (overhead reads high) though, probably because of my EZ.

 

with a corrected speedo (with my bdtd), running 35's, and my mods, my overhead reads 24 mpg...... i don't care how wrong it is, it makes me feel good just looking at it, with fuel nearing $4/gallon.

 

Mine always reads 2mpg high.At least its consistent.

 

Checked mine few weeks ago.Hand was 15.6 and overhead was like 15.4.

 

I stopped checking mine and i leave my overhead on the temp/direction other wise i just get

 

mine is always around 4 mpgs high.

 

It is sort of like a Dyno run. As long as you know your baseline at least you can compare as you make changes to the truck. And always use a calculator if you need to know the actual mileage.

 

mine is consistantly 3 high

 

mine is 4 to 5 high. do hand cal. always . odometer checks ok .

 

Mine always read with in 1 mpg UNTIL I started using boxes and programmers. I thought everyone knew boxes and programmers screw with the mpg on the overhead.
Any box that does pressure will screw it up

 

Hard to be accurate with hand calculated also.
Fuel density changes with temperature. You will fit more fuel in your truck in cold weather than hot because cold fuel is more dense.
What if you fill up at a station that does not have level ground. That will affect how much fuel you can fit in the tank. Truck pointing slightly up hill on first fill up slightly down hill on second.
Many things can effect your hand calculations