In a nutshell, my 6.7 averaged around 8MPG no matter what the driving conditions: towing 5K, running empty city/highway, didn't matter. Not long ago I made it exactly 147 miles from a full tank to half empty, all highway miles. Truck spent all of its short life on a set of BFG AT 315s.

I returned my truck to stock in anticipation of turning it in, put a set of half worn out OEM BFGs back on and made a 500 mile round trip to buy an '06 today. Noticed the fuel gauge wasn't moving in front of my eyes like ususal. Reset the overhead a couple times and it read 17.9MPG at the end of the trip. All highway miles running 70-75.

This makes sense, yes, but these exact same tires and wheels reduced fuel economy in my 04 by 15% or 3MPG at worst, it still got 18MPG most of the time. Figure that out, the day I go to buy a new truck my 6.7 starts treating me right. No MIL in 500 miles and I still have about 1/8 tank left.

I still bought the '06

 

Part of the problem is that the 315s do cost mileage and part of the problem is the pinion factor. If you did not correct for the larger diameter it would have shown worse than actual mileage.


John

 

I had it set to as close as possible, IIRC they can only correct for a 33" tire. speedo would read 70 truck would be going 74-75.

 

yeah, but a 10 MPG difference??? Sounds like that ol 6.7 is givin you the finger as it goes down the road

Chris

 

I think it has alot ot do with the particular tire. i get worse mileage out of my mt's than I did with my at's same size

 

Hovismo this isnt directed at you but it really suprises me how many ppl complain about mileage but then when you look at their rigs, they have 6" lifts and 37" tires and they just cant figure out what is going on.... Now to say that i do agree with you that a 10mpg difference is pretty friggin ridiculous in your case now matter what.

It seems that the 6.7 is decently efficient when just cruising without much load, but when it starts to get into the boost a bit due to towing, larger tires, heavy loads, it seems to start sucking the fuel more quickly then the 5.9 and obviously so as it is a decently larger engine...

How much peak boost does the 6.7 make?

How much peak boost does the 06-07 5.9 make?

Just curious.

 

49 more cu in, 25 more hp, 40 more lb/ft torque, and cleaner exhaust all contribute to variations between 5.9L's and 6.7L's.

Ironically, one can go over to the 5.9L HPCR forums, perform a search, and read countless threads of *****poor fuel economy. I'd imagine in some cases lots of 5.9L HPCR owner's fuel economy "went up" when the 6.7L's came out.

 

had I not had the exact same lift/wheel/tire combo on my previous truck I would not have been as surprised. my main point was that my 5.9 handled the bigger tires much more efficiently. stock tires are about useless for anything I do, will be going back to BFG ATs on the new truck, though not quite as big.

 

Averaged 8 mpg over how many miles? That 6.7 is probably still breaking in. Sure you won't get better mileage with 315s than OEM, but mileage will still come up as the engine breaks in.

 

first 5,000 miles.

 

I would've gotten rid of that truck too. That was 5,000 empty and loaded all at 8mpg. 14/15mpg empty would've been bad but bearable. Yeah 315's are gonna cut your mpg's but 8mpg is just crazy that ain't right at all...

 

I put my 325/70R17 tires on my 6.7L at 1700 miles and have 9000 miles now. My average fuel economy of the first 1700 miles was 16.7mpg. I am averaging ~14.5mpg now, unloaded. I pulled ~13000lbs. from Kentucky back to Texas (~1400 miles) and averaged 13.3mpg on that trip. This was with a box trailer too, so headwinds played a greater role than when pulling my flatbed g/n.

I honestly think hovismo got a lemon, plain and simple. I have seen some fairly clear trends with the 6.7L owners on this and other diesel forums since their release. Those that drive their 6.7L like a grocery getter around town have problems; those that work the truck don't have a problem. Hovismo seems to be the exception to this rule as he worked the truck (as it was intended to do) and still had problems. Some of his problems seem to stem from dealership incompetance but I also believe he has a lemon truck; hey, it happens.