I have read many post here about the poor mileage of the 6.4's. What I have not determined; Is the common thread among all these super duty's is "Electronic Shift-on-the-Fly"

My thought is energy is being consumed turning the front axle and drive shaft. Trucks with manual locking hubs and shifter do not expend this energy, thus better mileage. Ford obviously takes this feed back seriously, because they no longer offer 3.73 with 18" wheels.

Thoughts?

 

for some peeps 20 miles a gallon would not be enough. what are you calling "BAD"

 

Bad would be less the 14 mpg without a trailer, after breaking-in. I'll leave it to the reader to determine break-in.

Anybody who complaining about getting better than 18mpg out of 6.4 must also believe the oil companies bought the patents to motors that get 300mpg and hide them in Area-51.

 

I believe this would be the case with a full-time system, but this system is part-time. But my thoughts are along the same lines as yours; friction.

Some guys get great mileage, some get really bad. I can't say why one guy gets 7mpg while another gets 13 with the same truck, but all of my trucks have varied from what my neighbors get with theirs, to a smaller degree. Maybe 3-4 mpg. I think a big part of it is how tightly the motor and drivetrain are assembled, so luck-o-the draw on that one. No way to change that except run it. The other part is how they drive compared to me.

Some guys getting those real low numbers have legitimate complaints. Something wrong there for sure.

 

The front axles do not turn until you turn the dial and vacuum makes the hubs lock in.

 

The ESOF system work the same as manual hubs.
The front axle does not turn.

 

My thoughts are a few things. 1st the 6.4 Super Dutys drive train is heavy duty and tight causing extra friction. Same as the transmission is built so heavy duty to handle 24k loads. I did notice a difference in mileage after towing over 2,000 miles this summer and the truck breaking in after 5k. The manuals seem to get 2mpg better. Even in my 99 the manual was a heavy duty transmission comparison to what my Chevy 1500’s clutch and transmission were pretty light duty. Especially the 450’s are a heavy truck and it takes a lot of fuel to get 9,000# rolling and getting it up the hills. 2nd the 6.4 above 20#s of boost and 2,000rpms really eat up the fuel. The Dmax and Cummings do not seem to be as thirsty above 2,000rpms. So it comes down to if you want fuel mileage with the 6.4 go with a supercab instead of a crew. SRW, 3.55 gears and a manual. Also keep the boost under 20# and rpms under 2,000. With rural and hwy driving might see around 20mpg

 

I don't know about peeps, but my 6.4L is getting 12 mpg. That is bad!

The best I've heard, at the gas pumps (6.4L owners all seem to ask each other) from another 6.4L is 14 mpg.

I have the 18" wheels, how do I know if I have the 3.73 or not?

 

several things can be done about mileage. the last reprogram shuts off regen at idle so it is done more efficiently at highway speeds, another is keep proper air pressure, also keep idleing to a minimum. 12mpg is very good on a 250 with 11k on the odo. these trucks/engines are built so tight, economy sucks untill things start loosening up.

 

I believe most people are comparing the mileage of the 08's to the 07 and on down 6.0 powerstroke. If I am correct the 08's weight is more. Weight is a huge killer of mileage. How much more do the 08's weigh over previous years?

 

Could the mileage have something to do with the barometric pressure sensor? My F350 4X4 dually gets good mileage with less boost above 6500 ft in elevation. It get less mileage with more boost the closer I get to sea level.

 

I have reg cab with 7000 miles and get 17.5. The last time a towed was last year and got about 13. Xl bare bones truck auto. I'll take this truck anyday, it gets the job done.

 

bowtiehatr, "the last reprogram shuts off the regen at idle" Which is the latest re flash? I had mine reflashed in Dec. Has there been another since then? Thanks.

 

I had mine reprogrammed two weeks ago with the latest flash and it will still regen at idle. I stopped by the dealership today and there wasn't anything available that I haven't already done. Mine averages between 10.2 and 12.6 hand calculated and most of the variations are how long I sit in traffic per tank. I don't tow often and only have 10,250 miles so far so I'm sure I haven't gotten it broken in yet.

 

I have a job one 08' F350 4x4 short bed, ext cab PSD with 12,000 miles on it now. I just got back from a 7000 mile trip from Northern Ca to South Florida and back... I have a Lance model 815 2000 lb slide in truck camper on it plus extra fuel tanks, tools, 20 gal of water and so on including the kitchen sink, this camper is horribly aerodynamic. In town, with a lot of stop and go driving I average around 14 mpg or so. At 75 mph I averaged 10 mpg, at 65 mph I averaged around 13 and at 60 averaged 15. Note: I was driving North in Death Valley, CA (earlier this week) with a 45 plus mph headwind and looked at my lie meter (which seems to work pretty well and I trust it, also Fuel there was $4.77 a gallon at a Chevron) and averaged 4 to 5 mpg, believe it or not the truck seemed very stable with air bags and overload snubers I installed. Unloaded at 70 to 75 mph I average around 20 mpg (hand calculated). Note: I have the 20" wheel package with 3.73 gears and at 75 mph I am turning 1950 RPM. Note: I posted earlier tonight that I have developed a front main? oil leak on the engine... Changed my oil at 3000 miles and at 7000 miles using Shell Rotella T 15w40 CJ4, the manual says it takes 15 quarts with filter change, mine takes 12.5 quarts...