My main problem is that I'm always hauling something on, or behind the truck, and I have a canopy on tom all the time. Without the canopy it can do better. Having said that, I can get 17 MPG @ 80 MPG, that was pretty fun, these trucks smooth out nicely after about 65 . But its an event when I can run empty just for the heck of it.

My real world average is closer to 15 MPG when you factor in me holding pace with traffic, while hauling at anywere from 55-75 MPH. No idea what the truck could do on a more flat part of the world, or an new IP.

 

Yeah, I got 17 mpg once or twice (unless maybe I didn't get the tank all the way full LOL!). But that was pretty much all extended highway driving using the cruise to keep it at 60-65 mph. Definitely not driving around town. I guess maybe if you did ALL small town driving in a really flat area and kept it under 45 mph almost the whole time, AND you were REALLY disciplined about not letting the engine get abouve 1500 RPMs it might be possible to get a couple of mpg better than that, but I still have a hard time believing in a consistent 21 mpg.

Read the tuning with glowplugs thread. According to that mine was tuned and running so well that the guy who started the thread said not to mess with it. You can see my setup listed as the SOLD truck in my sig.

And I didn't drive it like Mario Andretti either. I might have been able to drive it a little bit easier some of the time, but you can bet your boots that with diesel somewhere above $3.50 a gallon I was NOT lead-footin' it at all!

And I consistently used addatives too. Either 20% bio OR Diesel Kleen at 150:1 - without exception. Both seemed about equivalent, mileage wise, though the B20 seemed to run a little smoother (and definitely smelled better).

All I can say to the "true believers" is you'd have to SHOW me to get me to believe it.

 

Diesel foams up a lot when being pumped, which I've found makes it difficult to get a truly accurate reading. The foaming probably varies widely from ambient temperature, fuel brand, flow rate, and God knows what else. So when the pump kicks off, it's hard to tell if I filled it to the same level as the last tank and I don't know if my mpg calculation is accurate.

The only way I know it's accurate is if I fill it all the way up to the filler neck, which I don't really like to do. Takes too much time.

 

The best I can manage for consistency is to look down the filler neck to see if the nozzle is shutting off from foam or real liquid. I've fueled up at the same pump since I got the truck 2 years ago, and always back off when I hear it reaching full, that controls most of the foaming tendancy. Can't fill at full speed anyway.

 

And therein lies the problems with getting accurate MPG! The only sure way is to fill the tank a cup at a time, burping the tank, until it's full right to the level of the cap. That takes about 20 minutes for both tanks on my truck! Who will take that much time filling up? Not me, generally. When I do take the time, I make sure it's a slow day at the pump so I don't have to endure the stink-eye of the people waiting

 

Most times I pull up to the pumps I am leaving 150 to 200 dollars in the cash register when I leave.
66 gallons of fuel capacity is nice, right up untill you have to fill it up.

Those other people are just going to have to wait.

Since I use mine for business, I always get a fuel reciept, and write the miles on it.
A spreadsheet makes it easy to get the MPG on each tank of fuel as well as an average MPG for the year.

In 2005 my max mileage was 17.14, my minimum was 4.39 and the average was 10.54 for the year.
Plowing snow 4.39 MPG because of all the backing up sure does a number on MPG averages.

 

....and that is the only way to figure out your REAL mileage - average it over time. The little inconsistencies of not getting it quite as full this time or getting it a little more full next time all average out when you start averaging mileage over multiple tank fulls.

ONE tankful calculating out to 21 mpg is NOT a valid basis for claiming to "get 21 mpg". There are too many variables that can throw the calculation off (underfilling, overfilling, heavier or lighter load, heavier or lighter foot, heavier or lighter traffic, unusually high OR low number of highway miles, more or less miles going uphill, etc., etc., etc.). You just can't justify the claim based on one tankful.

Like I said, my NA truck got just over 17 mpg a time or two, but the running average was 14-15 mpg in mixed daily driving with no load. I know this because I kept a spreadsheet like Dave is recommending. That is the only way to REALLY know what kind of mileage you're getting. I also did a spreadsheet for a multi-fillup average over a 2200 mile round trip hauling a camper in the bed and towing my Jeep. That is how I know that my "loaded" mileage was 10.3 mpg average.

 

A spread sheet makes short work of service intervals, MPG, cost per mile, tire rotation and any thing else you enter into it.

Mine has ever gallon of fuel, the price paid per gallon, odometer miles at the fillup time, parts numbers and dates, oil changes, tire changes and everything else related to my truck.
I started keeping everything on the computer in 96, so I have a good baseline on what is normal.

I can look at the sheet and tell when we go from summer fuel to winter fuel and back.


Makes it very easy to see that my operating costs would not make the payment and pay for insurance if I bought a new truck.
What good would a new truck be if I had to spend more than I am now just to drive it around the block once a week.

 

with my truck i usually do highway miles ( 130 miles round trip ) and i average 15 mpg and yes it takes me about 20 minutes to fill my truck up where there is no foam but fuel where i can see it in the filler neck. its a PITA to fill up that way but i keep close tabs on my MPG as thats is usually an indicator that something is not right if it drops low for no reason. now i usually drive 55-60(1900-2000rpms). but in the next few tanks im going to try running it at 65 to see if my mileage goes up stays the same or goes down. if it stays the same them i may start driving 65 again as im in the habit of driving that slow becuz my f250 had a 460 in it and man that thing was THIRSTY!

 

I don't mean to bring this back from the dead, but the naysayers compelled me to reply. Since I started this thread, I frequently break the 20mpg barrier. Here are some exact numbers from my last trip into the city.

Springville, UT to West Valley City, UT /// 51.2 miles (102.4 round trip). According to flying J, the quantity of fuel I purchased when I got back was 5.145 gallons @ $4.71/gallon. the trip cost me about 25 bucks. The truck was empty on the way up and loaded down with lumber and building materials on the way back. That's about 20mpg. I made the same trip last week towing a flatbed trailer and a 3,500lb car. Loaded on the way up, unloaded on the way back. The trailer probably weighs at least 1,500 lbs. That trip, I averaged a little under 17mpg. I drive 55mph and NEVER beat on it or floor it.

I don't see what is so hard to believe about this. I really do feel bad for those of you that don't come near the 20mpg area... that really is too bad. But just because you have never come close doesn't give you the right to call "BS" on others. My driving is fairly balanced with city/hwy and I have never gone below mid 15's on my truck. I am taking a trip up to Idaho to get a car on the 4th of july weekend. This is about 800 miles round trip... I'll do an average and report my results when I get back.

 

what gears are you running? the BEST ive ever gotten and it has only been one tank was about 21mpg BUT that was easy on the acceleration (which i normally do as i try to ease it to shift in the 1500 rpm range) and i drove only 50 MPH down from my usual 55-60. on average i still get 15mpg which isnt bad but as easy as i am on throttle 20 mpg should be accessible...

 

mine is easy 110 miles per day... 12-13 mpg buttttt that is running 70-80 and running 2800-3400 rpms' with 410's and 265's hypermax turbo... if I would stay around the 1800 rpms I would be doing about 45 mph..man I need a overdrive instead of this underdrive...(locked in high side 1to 1 )

 

Not trying to torque you off, John, but why can't we say "BS?" Maybe sometimes we disagree a little more impolitely than we should. I know I was a bit testier than I should have been at the beginning of this, which I regret. But bottom line, you're free to do the same thing any time you like when YOU disagree with US.

There's a pretty diverse group here with a lot of miles under their belts with these trucks and what you are claiming just doesn't compute with most of us. It's the equivalent of you saying, "The sky is pink, dangit!" while we're standing next to you, looking up and seeing blue. I don't think any of us called you a liar but your mileage could be inaccurate for many reasons including an inaccurate odometer and all the problems associated with fillups. David85's truck is built about as MPG friendly as it can get and he can barely get where you claim to be hauling loads at 4000+ feet.

Also, there is a slight chance you are correct and you can help settle our minds on this by giving us some data and to see how it stacks up. With answers to the following questions, we can get a good idea of how accurate your speedo is, which is step one in finding out how accurate your mileage readings are and get us to back off a bit. Maybe even eat crow.

1) Which trans?
2) What axle ratio?
3) Tire rolling radius of rear tire (from ground to center of hub)?
4) What is the color of your speed drive gear?
5) 60 mph tach and speedo readings?

 

As it so happens, the weekly route I drive lines up with two addresses on google earth, so I was able to use the "directions" feature to verify the accuracy of my speedometer. I checked two slightly different routes and they both matched my trip meter perfectly.

So far, I've peaked at 21.5 MPG averaging 70 MPH completely empty. If he is indeed staying at 55 MPH, than his claims are possible. But it would help some of the skeptics if we knew more details about the truck to make sure that the results are accurate. I recommend GPS or google earth to verify your speedometer.

These truck can certainly reach 20 MPG under the right conditions, and I know of others that have done it. But it won't happen above 2800 RPM.

 

Fair enough. I don't know many of the specifics of the top of my head, but perhaps you can fill some of them in before I can get home and look at the truck. It's an 86 6.9, 4wd. It has a 4 speed manual and I am willing to bet that it has a pretty crazy towing ratio. My tachometer bounces like a jack russell terrier, so I don't really know my rpms, but when I am at 50-55mph on my odometer the engine feels like it's in it's sweet spot... any more and the engine sounds over stretched and I can see some black coming out of the exhaust. I think my speedo goes to about 85, but I'd never take it that high. The engine has about 75,000 on a bottom end rebuild and the truck has about 335,000. I've got some pretty big tires on her, although I doubt the tires are much taller than the factory steel wheels. My Garmin GPS shows me that my speedo is about 5mph off... speedo says 50, I am going 55. I rarely even look at the odometer... only for oil changes. When I figure my efficiency, I either use my gps or figure the exact miles for my route on mapquest or google. To minimize differences in fueling, I use the same fuel pump/nozzle at flying J every fill up. I put it on it's maximum setting and when the nozzle pops, I let the nozzle drip for a few seconds then remove it. Stick it in the auxiliary tank filler and repeat the process. Even if it does foam, I doubt the differences are much more than 1/4 gallon give or take.