For you who are daily readers you will know that I went to OKC to pickup my RDS fuel tank today. It is about 140 miles each way once I get on I35. So, when I got up to speed and on cruise, I reset the fuel mileage. After driving the 140 miles I had averaged 15.5mpg. That was running 70mph straight into the wind, no regens, and one stop at the toll booth. I don't know what the wind speed was but if you have ever driven through OK ans KS you know it is pretty strong. So I picked up the tank and was back on the road in the opposite direction in less than 30 minutes. As soon as I got back to 70mph I reset the fuel mileage. So on the way back when I got to the same place where I had started, my average mpg was 20.2. Yes, 20.2mpg for over 140 miles in my dually running 70mph. I noticed on the way down the boost was around 8psi. On the way back it stayed at about 5psi. Also the EGT ran about 50 degrees cooler with the tailwind. So that is how much difference a strong headwind/tailwind can make. By the way, on the return trip I gain about 400' in elevation too so there is more uphill.

 

That's better than my '06 F150 5.4L gasser...I average 14.5 around and on long trip, I can squeeze 15 out of it....and I never really travel more than 70mph...always on cruise on the highway.


That's incredible to get that kind of mileage in a big ol' heavyweight CC dually. Unreal.

 

Just think of how great the differences in MPG would have been had you been towing your 5th wheel.

 

Headwinds are a really sore subject for me! I get angry almost every week. I have the nav system and can pull up the weather which shows the ground wind speed and direction.

Every week, I head out either north or west when there is a weather system moving in giving me 10-17mph headwinds. One or two days later, the system has passed and the prevailing winds behind the system give me a 10-12mph headwind from the south! Drives me batty! I'll get 9mpg into a headwind towing my trailer and I get hit with it coming and going. Really grinds my gears.

I drive to Shreveport tomorrow and I'm hoping for a mild wind from the south followed by a strong tailwind from the west as I head toward Florida on Tuesday. Then a nice prevailing wind from the west as I head home from Florida to SC on Wednesday.

With my luck another cool front will fight me Sunday and Wednesday! It's rare down here to have easterly winds but when it happens it's usually strong and brings storm warnings with it.

 

I think that you have passed the "magical truck" test and can forever claim, "My truck does 20+ mpg all day long". No need to get into the discussion of head wind, stopping for gas, lunch, truck speed, or regen.

More seriously, a few weeks back, I took a 3 hour drive with a 30+ mph tail wind. Could be the best ride I've ever had in the truck. In most cases, seems like I'm always driving into the wind. I don't care about mileage that much but driving into a strong wind gets old quickly.

Congratulations on having one of the magical beasts. Don't ever sell it. doesn't give these magical trucks to just anyone.

bruce....

 

Tracey did state that she reset the odo after being up to speed and possibly after the engine was up to temp. When I give my mileage round trip it is from the get go. Cold engine and getting up to speed and temp. That to me is real world. Tracey's objective wasn't to show great mpg's but the diff. in mpg's with a tailwind vrs. a headwind.

 

Was just kidding around, nothing serious was intended.

 

I could totally see a 20.2 MPG run with a tail wind in the 6.7. I achieve 18-19 MPG hand calculated in my 16 year old 7.3 on a regular basis. I would certainly think that the newer and more efficient 6.7 could do the same or a little better with the help of mother nature pushing you down the road.

I must note though, I cruise at 65 MPH on the interstate, so at 70 MPH my MPG would be a bit lower than 18-19 I am sure.

 

Since you mixed in some apples with the oranges I'll add a few plums. My 6.0 got consistently better highway mpg's than my 6.7. 21 mpg vs. 16 mpg. Diff. being a 4 by 4 vrs. a 4 by 2 and f-250 hrs. f-350. However the power difference is night and day. I loved my 6.0 but the 6.7 made me forget her.

 

Your absolutely right, but the way I saw them as being similar vehicles is because of the overall weight and size. I'll step back away from the conversation now and just watch from the sidelines.

 

My '99 7.3L and '15 6.7L seem to get the same mileage on the highway unloaded. They are identical except for year. Stock F350 Lariat 2WD DRW 3.73. On both of them the indicated mpg is about 1 mpg optimistic, and the speedometer about 1.5 mph optimistic at 65. Both get 19 mpg on the same road, same trip, 65 mph, hand calculated, multiple trips. If I get a regen on that particular trip (180 miles) it knocks about 1 mpg off the average. Mostly highway with a little bit of on/off into town. Haven't run the '15 loaded yet to know how they compare loaded.

One day driving north on 101 into about 35 mph headwind with the camper, I could not use 4th gear in the 7.3L, drove all day in 3rd at 55mph, that was a long day. A big advantage of the 6.7L is the 6 speed doesn't have the big hole between Top and next gear.

 

I have run that strip of I35 many times. Usually down around 8mpg into the wind and well over 11mpg coming back.

 

I had a 6.0 that was almost identically equipped as my 6.7L. The 6.0 had a 4.10 gear and the 6.7 has a 3.73. The 6.0 got better mileage in town and on the highway. It got about the same as my 6.7 towing. There is no comparison though when it comes to the performance of the 6.7 over the 6.0.