My overhead was consistantly off by as much as 2mpg with every tank. Then switched jobs, and switched driving. Went from trips of no more than 20 mins, some highway and some city, to trips of an 1hr15mins almost all highway. When that happened, the overhead all of a sudden became accurate.

 

just cheat the system...

Find a long hill, put truck in N, roll truck down hill ( leave engine running ) hit reset before coasting, I can get up to 37 mpg !!!!! on my patial drive home.

I will post pics of my awsome mileage .......

 

I agree with Foiled above
that if you use the gas pump number to calculate MPG
the calculations are still not 'perfect'
because it is impossible to refill to the same level each time
because trapped air inside the tank causes level variation.

You can reduce this a little
by 'rocking' the vehicle and trying to put a little more fuel in.

 

you make it sound very complicated. it is actually very accurate if you do this:

see how much gas you pumped. for example, 20 gals.
lets say you drove 300 miles. then divide the 300 (check your odometer) by 20. TA DA!! simnple as that. and that is the most accurate you can get!

i underatand what you mean by the air but thats barely any air at all! thats not gonna affect it that much.

 

i know this post is old, but i am curious, my mpg is way off on an 06 dodge quad cab,if i look at the "distance til empty" when the tank if full, it shows the the milage as if i had a 26 gallon tank, but i have a 35 gallon tank, would this affect the MPG shown on the other setting???

 

The only way to accurately check mileage is fill the tank absolutely full (not good for the evap emission system), drive it a while, then fill it absolutely full again, then do the math. Air in the tank must be "burped out" by rocking the truck. It would also help to stop at a pump where the truck leans away from it a bit and is nose down. All a bit picky, and as I said, not good for the emission controls, but if you want definitive results, that's the way. You can't count on the pump cutoff to be accurate enough. I guess if you fill up at the same pump every time, you'll get a pretty good baseline.

 

Won't affect MPG -- that's a rate of consumption, the computer "knowing" how much fuel is being used and number of miles driven. How long have you had the larger tank? I read another post somewhere that the computer would learn the bigger tank. Hope that's true. BTW, remember it costs fuel to carry fuel. That extra nine gallons of gas weighs about sixty pounds. I let my truck get down to a quarter-tank, then put half a tank in it unless I expect to drive a long way immediately. Just for the commute, I don't make it accelerate all the weight.

 

The filling up halfway idea is a good one. Except I usually try to keep mine somewhat full in the winter, gives me a little more weight back there.

 

The filling up halfway idea is a good one. Except I usually try to keep mine somewhat full in the winter, gives me a little more weight back there.


[/quote]
Reduces the condensation, too.

 

So I know I am going to sound dumb. But the overhead calc is hit or miss? I used mine on the first full tank and the distance to empty seemed to be right on.