I love my overhead computer, but it lies to me. If I believed it, I am getting 25-27 mpg. But when I do the math, it is typically about 5 mpg lower. When new, the overhead did a good job of estimating my fuel economy, but now nearing 100,000 miles the error rate has been gradually creeping higher. If I keep it another 10 years and 100K I might even be getting upwards of 40. That would be something to really brag about.
Are there any ideas of what might cause this upward creep in reporting fuel economy? Is there a way to recalibrate the computer to I get a more realistic estimate?

 

It's a common issue. If you do a search on mileage/mpg you'll find that it's a common complaint.

I know of no way to recalibrate the overhead, and even then it's doubtful it would ever be accurate.

 

If you adjust your tire size with a smarty, it will adjust your overhead read out. Tire size will effect it also. Say it takes 5 gallons to go 100 miles. If you put on bigger tires, still takes 5 gallons but the bigger tire travels farther with each rotation so you truck may only think you went 95 miles using the same amount if not more gas.

 

I thought about mentioning the tire size changes, but he didn't mention any changes to his truck . . .

I have the Smarty Jr. and have adjusted my tire size, but the mpg is still off.

I believe the changes the Smarty makes to the computer messes with the lie-o-meter inputs so it's most likely never going to be accurate. I remember testing my Smarty out early on - the faster I went (>70 mph) the higher my overhead mpg reading went. If only it were true!

 

The more you reset it the less it's accurate...

Get A scangauge II they are very Good for this

 

The over head guesser (otherwise known as the 'Lie-O-Meter') is good for the outside temperature and compass, and that's about it.

 

^^^^ Exactly.

I've owned my 2004 since new and I have never used the fuel mileage monitor on it. Nor any of our other vehicles.

The only accurate way to calculate fuel mileage is by manual calculation using fuel used and miles travelled.