I just returned from a round trip (empty) of 1,440 mi from MO to GA. I drove most of the trip with cruse set on 77-78 mph. For the total trip I averaged 17.2 mpg...this includes 100 stop an go miles driving in Atlanta, and about 2-3 hrs of stop and go in highway construction and a bad traffic accident. My best tank was from Dalton, GA to St Louis, MO...490 mi at about 77 mph and 18.6 mpg. These numbers are hand calculated. I hope that I may get a little better mpg when I change to full synthetic, and drive closer to 70 mph!!!

 

I do know that for the entire time I owned my truck, the hand calculated and the computer were very, very close....like within .3 to .4 MPG of one another. I always hand calculated too but found that the computer was much more accurate than those in the older trucks like my '05.

 

Only had mine for about a month - roughly 2800 miles... I live in TX hill country and that causes me to suffer - constant pedal - I idle a lot for dog who live in the back seat - Ranch is like city driving - stop & go, in town a lot also...

Best tank mileage - hand calc - 16.43 - mostly straight highway 70-74 mph..

worst - hand calc - 12.65 - 200 miles at 84 mph toolbox/cab full of personal gear...

Overall - right now all miles /all gallons 14.12 -

But - that running 80+ out to west TX and pulling a trailer in 4x4 though modest mountains is not a good test for everyone... I don't even do it regularly

My computer and the truck computer are at least 1 mpg difference...

 

I reset the mpg thing when the new tires (35/12.5/18or285/75/18) went on and have just over 6,000 miles since. Dummy thing tells me I am averaging 17.1mpg. Every once in a while I do a hand calculation which comes out just a little better than that. So to me it is accurate enough to say I get 17mpg. My driving is hill country with a sprinkling off tar and on hiway. I am also an aggressive driver. I happy with the mpg's this thing is giving.

 

On my '11 dually 4x4 in long, 1800 mi. Trips through the mountains of WA, id, and Montana it was averaging right about 17. But that's lots of mountains and driving at 75. I try and always keep it below 75 for mileage. 65 is even better, but would take too long. Yet driving 25 miles from my house to Seattle mostly on I-5 I can get 20.5. Towing the 40' 15500lb 5 th wheel, get between 11 and 12. But in town is way down in the 15 range. But still a bit better than my '10 250 set up the same way except axle ratio of course. And better than my Dodge Dakota with the gas v-8! And o much more truck!!!
Every time I check my hand calc. Against the comp. I get about .4 better with the comp. But speedometer is 3% off too, so actual and comp. Is pretty close. Now to figure out how to calibrate the speedo better.

 

My truck always matches the hand calc within a couple tenths. The key to remember though is that the mpg meter shows the mileage the truck has gotten since it was last reset. If you don't reset it at each fillup and only at the fillups, don't expect the two to match. Modern vehicles are extremely accurate at measuring fuel consumption. They have to be to meet current emissions standards. Most vehicles even have fuel temp sensors now, since temperature affects the specific gravity of the fuel (a given volume flow provides a variable mass flow inverse with temperature). Hand calculating a tank where you are relying on the station's pump shutoff feature (an no temp compensation), even if you're at the same exact pump parked in the exact same orientation, etc, is very likely to be less accurate than this.

Regarding when you reset the meter during your trip, I've done it both ways. I often reset several times to see what I'm getting in specific conditions and purposely leave out the cold start. The key point to remember is that the meter is only accurate across the distance between resets. When it comes to resetting before getting up to speed or after, as in the example discussed above, it really doesn't matter much if the distance is short. I've done it both ways and the difference falls within the normal noise. Consider what a running average is in the first place. If you're getting 20 mpg for 20 miles, but getting 5 mpg for the first 500 feet, it doesn't have much of an effect on the total average. Same goes for flooring it to pass someone briefly. The very short distance that those conditions exist for make them insignificant. In the case of the 5 mpg for 500 feet/20 mpg for 20 mile example, the difference is 0.08 mpg. It's basic math, there's no magic.

You obviously need the distance between resets to be the vast majority of the trip or the result is not indicative of the whole trips average. As long as the appropriate disclaimers are given people should be able to share and compare these numbers. Like any other tool, the mpg meter is only as good as the person using it.

If it's fairly safe to assume that fuel consumption monitoring is accurate, that leaves odometer accuracy, which is a valid concern. The mpg calculation will be off by whatever that is off, but so will your hand calculation.

I've been into "hypermiling" for many years and could go on for hours about it, but I'm sure I've done enough damage already. Sorry for the length.

 

Don't forget about the dreaded Regen, show that mpg when that babies cooking.

 

I have posted many times on this site that my mileage is very dependent on the quality of the fuel. I use PM22.

Driving round trip from Houston to San Antonio recently I averaged 21 MPG for the trip, many of those miles had a 75 MPH speed limit.

Just got back from Pensacola Florida (started out in Houston) and averaged 18.8 MPG, also at 75 - 80 MPH. Mileage was impacted by keeping the truck running on hot days, to keep the AC running.

My commute to work includes 10 miles traveling at a speed of 65 MPH, the other 5 miles is city. I am disappointed if I cannot average 18+ MPG per tank.

The truck has 57,XXX miles on it and I can say four things definitively. It likes to be hot (warmed up), it likes PM22, if I get a poor quality of fuel I can tell in a short period of time and if I let it idle the mileage will be poor.

 

Yes, that regen will take me right down to 9-12 empty pretty quick for that period if about 45 min. What a way to kill mileage!

 

My dash pic is accurate, that is from my driveway in the suburbs, through the city, to the parking lot at work. Including traffic. I have found 17-19/19-23 that you posted very accurate. The "lie-o-meter" is pretty damn accurate to for lying.

It all depends on the terrain and driving habits, IMHO.

 

Agreed. Mine is also accurate and the second photo was a long round trip through varying terrain, conditions, speeds, etc. It was the average over a 769 mile trip which was conducted over a period of four days. The hand calculations on each tank were extremely close to the truck's readout, as I mentioned above.

As for the MPGs during regens, yes it drops. Anyone with an ounce of common sense knows that. Both of those trips I posted above included numerous regens during each and the averages in the pics speak for themselves.

I find it humorous that so many who seem to get less than stellar mileage like to claim that anyone getting better mileage than them is lying. I guess misery loves company.

 

I have kept track of my last 40 fill-ups and 10265 miles on Fuelly.My driving consits of about 55% highway,35% city and about 10% towing an 11000 lb fifth wheel.My average mpg are 15.7,my best tank was 18.1 and my worst was 13.3.My lie o meter has never been off more than .2 gallons per tank.
My truck is a 2012 F350 SWB,18 inch tires and 3.31 rear end.

 

Powerstroke72,
yes, I do have at least one ounce of common sense, I think, and I realize the mileage will drop during a regen, just didn't think it would be by that much. About half. Didn't drop that much on my 2010.
Not as bad as our new firetrucks where since they really never drive on the freeway for long, or anywhere for that matter, we would have to run them at hi idle at the station for 25 min. Not sure how that helped the environment!

 

I'm a little late to this party, but make sure to check that your hubs are not locked. A friend of mine bought himself a 2011 F350 CC LWB 6.7L and experienced exactly what you're talking about: ~13.5 mpg. While driving a different vehicle behind him from one ranch to another, I noticed it looked like his front axle shafts were turning. When we stopped at a gas station, I hopped out and looked, and sure enough they were turned to Lock. So I flipped them both back to Auto, and his mileage jumped up to 16+.

Just another thing to look at...

 

For me regens never drop my average mpg enough to notice, my instant mpg drops for about 10 miles but not the average.