6.7L Mileage

[Coalsmoke]

thanks regarding the info about the 6mpg with the hemi in the dually.

 

[WDixon27]

that makes me feel better about my 16. 5-17, i beat the crap outta mine :-laf , about the only thing i do to help mileage is try to keep it under 70 on the interstate

I have to admit that i drive like a old lady to get the 16-17 and i dont have much weight in tools 300-400 lbs. But the price of diesel is getting to me :{ . Mabey a 6. 7 and 6 speed auto will at least match my current mpg? Im tempted to order one this spring. I could never go back to a gaser after a cummins.

 

[jcarey]

With our last gasser truck ('99 GMC) we got 11. 5 mpg highway empty on our last trip with the truck.



With our Cummins we have gotten a low of 16. 5 and a high of 19. 1.



Both trucks were/are 4x4.



Even with the price of diesel going up, the mileage difference between a gas engine and a diesel engine is still significant.



Also, in our area, diesel is still cheaper than the high test gas that we had to use in our GMC. (We could run the GMC on low test, but there was a lot of pre-ignition if we did. )



Jim

 

[betterthanstock]

Diesel contains about 15% more BTU, so even at 15% higher price, you will be ahead with the diesel. They get about 40% better economy than gassers, especially driving around empty. And loaded, gassers need premium, or much colder spark plugs to keep from knocking. Then after towing you need to put the regular spark plugs in to keep the cold ones from fouling.

Diesel is always running lean, gassers are stoichiometric (actually richer than optimum) so that the catalyst has enough excess fuel to oxidize. At WOT they run very rich, to protect the catalyst from melting, so on one hill towing you can easily burn twice the fuel of a diesel on the same hill.

Gassers get away with polluting more at WOT, except you don't see smoke, you just smell the raw gasoline--diesel smoke makes for good TV shows, but you can't film gasoline vapors, so CARB and later the EPA declared diesel exhaust a carcinogen, but not gasoline exhaust!!

 

[jcarey]

betterthanstock,



Thanks, very interesting, very informative.

 

[FPettijohn]

EB

I am sure the reason that 1st gear is so much stronger is the 4:10's and the double overdrive 6th keeps your rpms the same, wonder what a 3:73 or 3:91 would do for mileage. I pull 13500 loaded and only get 10. 5 best and usually 9. 5 hand calculated, so you guys getting 18 + must be working for the same people who figure bushels per acre and EPA mileage on the sticker . Just waiting for the 3500's with the new 6. 7 and the 68rfe.

Fred

 

[EB]

I was coming back from a job the other day and thought I would run a little fuel mileage test according to the speed I was traveling. This was all done on a smooth straight road with hardly any hills at all. This was done using the overhead computer, not hand calculated.



On one part the speed limit was 60 mph and I ran 61 mph for 19 miles, I had reset the mileage meter at the start and the figure was 12. 7 mpg pulling my empty 7600 lb trailer.



Next was at 67 mph for 20 miles and the fuel was reading 11. 8 mpg. Nearly 1 mpg more for 6 mph.



Next was 70 mph for 20 miles and the overhead was reading 11. 2 mpg. We all know that the speed makes a lot of difference in fuel mileage, but I sure didn't know it made that much difference. The bed on my truck is a skirted bed and I wonder if I had an open type bed where the air can get out from under the truck would make any difference. Does anyone have an opinion on that? A pickup type bed might do better than mine does, then again, it might not.

 

[Mel Swanson]

Thanks EB. A lot of good info. I can't get a price out of my dealer for a 2500 with the new CTD and Aisin trans w/e-brake. Do you recall what the extra charges were for these three items?

 

[Jaysyl]

There will be no 2500 with the aisin tran. The aisin is only offered on the 3500, cab and chassis. The 6 speed auto will be an 68RFE on the regular pickups with the beds. 2500s and 3500s.

 

[JBlock]

Interesting I 13. 8 to 14. 5 towing around 8000-9000 with 2001 4x4 auto on the highway, that open trailer with bed full loaded and Kubota tractor plus the attachment on the trailers, the other haul was with my 42 Packard limo at 7500 pound , plus the truck be full packed again. So i was over the factory cgvw for the auto. interesting thing was empty was only at best a little above 15 mph on the same trips. i running 3. 54 in OD on the flat and third and second in the mountain through GRants pass area,

 

[EB]

Thanks EB. A lot of good info. I can't get a price out of my dealer for a 2500 with the new CTD and Aisin trans w/e-brake. Do you recall what the extra charges were for these three items?

When I got mine the engine was the same price as they were charging for the 5. 9, $5,555 msrp. Jaysyl is correct, the Aisin is for the cab and chassis model only, I have no idea what the 68rfe is going to cost. The e-brake was $300 when I got mine, I understand it has had a price increase since then, up to over $400 now. Still worth it if you do any towing at all.

 

[dpuckett]

Your MPG numbers make me appreciate my 1st Gen. I got 15mpg empty (7200# with my lard behind in the seat) last tank in my 92. 5, and pulled the pump and sent it off to get rebuilt. I have seen 22 with this truck, and want to see it again.



When I was hauling hay, I averaged 13-14. 5mpg with a GCVW of 22-24K. 1993 D350 C&C, 5spd, 3. 54 gears. Never had to downshift unless traffic got too slow. Just because you havent seen the numbers in your specific rig doesnt mean it isnt possible.



Daniel

 

[Coalsmoke]

Your MPG numbers make me appreciate my 1st Gen. I got 15mpg empty (7200# with my lard behind in the seat) last tank in my 92. 5, and pulled the pump and sent it off to get rebuilt. I have seen 22 with this truck, and want to see it again.



When I was hauling hay, I averaged 13-14. 5mpg with a GCVW of 22-24K. 1993 D350 C&C, 5spd, 3. 54 gears. Never had to downshift unless traffic got too slow. Just because you havent seen the numbers in your specific rig doesnt mean it isnt possible.



Daniel

That's a good point right there, with the new engines will be new aftermarket tech and knowhow. Hopefully Piers will get back on the pump-building train

 

[Champane Flight]

mileage

My old 95, two wheel drive/,3. 54, five speed, gets a solid twenty to twenty three empty. Loaded with 30' fifthweel, and a 17' boat behind it, I have never gotten less than twelve. That is pulling the mountains most of the time. I have not run it fully loaded since putting the plate in it, but have seen 6500#s a couple of times, but not loaded through a whole tank. . Still gets the same empty, if I keep my foot out of it. . Around eighteen to twenty solid. .



I think the ten from the unbroken in 6. 7 loaded is pretty good. Are you running synthetics yet EB?

 

[EB]

I think the ten from the unbroken in 6. 7 loaded is pretty good. Are you running synthetics yet EB?[/QUOTE]



Not yet, I'll put 18- 20,000 miles on it, then switch over to Amsoil.

 

[jcarey]

That still seems to be very good mileage since you're still breaking the engine in and you're running with 410's and not 354's.



I wish they made 354's an option for those who don't tow as heavy.

 

[MCummings]

No, its a not-so areodynamic rig and weighs just shy of 11,000lbs constant. From my experience, this would be about equivalent to pulling our 6,000lb 5'th wheel with an otherwise empty 2nd gen.

8 more tires rolling on the ground, and a longer rig make mileage worse.



I figure 10MPG is great for how he is working the truck. Our '05 gets about the same mileage in the same situation, and can easily get worse. With a Smarty, Magnaflow, and AFE intake (stg 1), we can get 9MPG loaded and get about 20. 5 unloaded.



Merrick

 

[Champane Flight]

Count on it

Yea, and that mileage will come up a little after the synthetic change also. I gained an average of two MPG after my change. . That would be a darn good number for a loaded rig...

 

[barbwire]

3:73s ?????

the new truck is with the 6. 7 engine, Aisin transmission and 4. 10 gears.

Can 373 gears be gotten with the 6. 7eng. & Aisin transmission ? Or is 4:10 the only option?

 

[EB]

With the cab and chassis you can get 3. 73 or 4. 10 gears with the manual 6-speed transmission I believe, I'm not positive about that, but I believe that is right. The Aisin is available only with 4. 10 gears.

It is my understanding that you will be able to get either 3. 73 or 4. 10 gears after the first of the year in the pickup model, not the cab and chassis with either the six-speed auto or the six-speed manual. Someone correct me if I am wrong.