Just returned from a mini family vacation, hand calculated 3 tanks of fuel were 17.38, 17.85, and 17.52. The overhead console showed around 24 to 25 mpg each time. Is there anything that could be done to calibrate the overhead to be reasonably accurate? Or just learn to live with it and use it for bragging rights with the gasser truck crowd?

 

Use it for bragging rights

Mine actually got much closer when I started to use the Smarty Jr. Most say the opposite but mine was always about 4 MPG off and now it is closer to 2 MPG off

 

Its called a lie-o-meter for a reason. At this point there is no way to calibrate it.

 

oversized tires? what was your average highway speed?

hand calc: I get 17.5 - 18.0 mpg all day long in mixed city driving... freeway I can get 23 mpg if I stay about 65mph or less.. overhead is always 2-3 mpg higher.

but I'm stock and 2wd..

 

My 6.7 is only about 1.2 miles per gallon off on highway MPG. Interesting at the difference with different years. I have been keeping logs for the whole 138k. It was off before tuner and after the tuner but remains about the same.

 

Mine is off about 17%, with or without a tuner. It may be 15% stock, but never run enough tanks to tell. Its annoying thou, as it varies from about 13% to 28%.

 

Your tuner is throwing it way off

 

My overhead says 18.4, but hand calculated is 16.3. Stock 6x6

 

Hand calculated my overhead is off by about 2 MPG on the plus side. I also heard that our overheads are not calculating the average MPG but the actual MPG you are getting at a specific point. Someone please correct me if I am incorrect.

 

I have a 05, 2500 2 wheel drive.
i just got back from a 600 mile trip
display said average of 22.6 mpg
i filled tank and figured the mileage at 21.8
only thing non-std was the vehicle has a K&N air filter, but its dirty and needed to be changed.
average speed 60-70 mph

 

empty the overhead in my dually reads about 2 mpg more than the hand calculated fuel ecinomy. While towing the overhead will be 3-4 mpg above actual.

 

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Description of the overhead console per the manual if it's any help:

The EOM provides several electronic functions and features. Some of the functions and features that the EOM supports and/or controls, include the following display options:
• Compass and temperature - provides the outside temperature and one of eight compass readings to indicate the direction the vehicle is facing.
• Trip odometer (TRIP ODO) - shows the distance travelled since the last trip computer reset.
• Average fuel economy (AVG ECO) - shows the average fuel economy since the last trip computer reset.
• Distance to empty (DTE) - shows the estimated distance that can be travelled with the fuel remaining in the fuel tank. This estimated distance is computed using the level of the fuel in the tank and a weighted average of long term and recent Average Fuel Economy.
• Elapsed time (ET) - shows the accumulated ignition-on time since the last trip computer reset.
• Blank screen - the compass mini-trip VFD is turned off or in Blank Screen Mode.

 

My lie o meter is way off. Always has been.

I handcalc a tank at 17mpg but the lie o meter will peak at 22.6 for the tank.

I don't try to understand it. Frankly I ignore it on the mpg feature except to use it as a running indicator for optimum speed on the road.

I always reset the trip odo and the time feature. But I leave the DTE and mpg alone. Dte always shows 620 after each fill up.

 

I'm running 285/70R17 tires (I think, one size larger than stock) on the stock rims. Speedo reads slightly off, 70 (mpg indicated is 74 by the gps). I have played around with the different tire diameters on the programmer I running this is the closest I can get it. The speed limit on the interstate was 70, ran 75ish. hope that helps fill in the blanks.

 

That will make a large difference in your OH readout, and probably why its higher than normal.

Your tuner should allow you to get closer than that, thats more of an error than it should have for the stock setting and 285's.

Looks like you can dial your tires in .5" increments.