A curious thing has been happening. For the first couple of years, my overhead compared to hand calculated fuel economy has been fairly close.
As I get more miles on my truck, now 40K, the overhead seems to overestimate my actual mileage. If I drive sensibly I typically will get 20 and change and the overhead will read 22. It us usually 1.5 to 2 mpg off.
Can it be recalibrated? Have others had similar results--particurly the change in accuracy?

 

uh 99% of this site never trusts the overhead cause its always off, nothing you can do about it.

 

I have been keeping track of my mileage on a Excel spreadsheet since new. I start a new file every year to keep the list small. What I found interesting was the overhead for last year was the usual 0.5-2 mpg off, but the whole year average, hand calculation was 15.6 and the overhead average was 16.6. I figure the overhead depends a lot on when you reset. I reset the overhead at every fillup, and use the temperature & compass display.

 

I'm like Fox & reset overhead (all funtions) at every fillup.
I record O/H & hand calc mileage.
When running empty my O/H & hand calc are usually within ~0.5 mpg of each other.
When towing 8000# 5th, the two values can vary 1.0-1.7 mpg
Go figure!

 

mine is off by 3 usually, and sometimes as much as 4.

 

I don't see how the overhead could ever be correct when it uses a number like 99 mpg to calculate an average. The truck will NEVER get 99 miles per gallon.
Lets say you start out with 30 fresh gallons at the top of a 12 mile grade. Make the 12 miles at 50 mph and the overhead will read 99 mpg all the way down.
Now finish the 29 3/4 gallons off with normal driving at 16 mpg. When the tank is empty the overhead will read 23 mpg, and you really got 16 mpg. I think it would have been more useful for them to put an instant economy gauge in place as opposed to a average.

 

My overhead reads 17.5. I don't want to know what it really is. Ignorance is bliss.

 

My truck did EXACTLY the same thing! Was accurate when I bought the truck, now it's nowhere even close. When I'm unloaded, it can be as high as 4-6mpg optimistic, and when towing, it's around 2mpg optimistic. It'll read mid-20's when I'm really getting high teens.

 

The 2nd gens have instant AND average. why they got rid of that i will never know, i LOVE having both in my '01...

 

x2, same exact here. Mine was always real close when new, but now is usally about 2-3 mpg high. I first remember noticing it after I had a flash done, so I wonder if that had anything to do with it?

 

Mine's never been flashed (unless dealer did it sometime without my knowledge, but I doubt it). I think I noticed mine change around the same time that ULSD hit the pumps.

 

I`ve never tracked mine very closely , but the last few road trips I have...it`s about 1.5-2.0 MPG too high.

 

I use the needle method when it hits the E its time to fill. MPG's is what it is. I know we want ever we can get but if it causes me to do a spread sheet then I'm going to have to sell this beast.

 

Amen. Stopped caring about MPGs because either way, when it hits E, I'll fill it up anyway.