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View Full Version : fuel mileage w/ Duramax



bigdob24
06-06-2009, 05:56 PM
I have a 2006 Chevrolet w/ 6.6 Duramax and Allison Transmission. I am looking at a Sundance 3300 RCB and would like an idea on what to expect with fuel mileage on one of these larger units.
Right now I pull a 19' toyhauler and get anything from 9-12 depending which way the wind is blowing :-)
Any input would be helpful.
Thanks
Dan

sailorand
06-06-2009, 06:08 PM
Dan
Last year I towed from Palm Springs, Ca. to Vancouver BC. I got 12.2 mpg keeping the speed at 60 mph. Just came from Vancouver to Seaside Or. at 12 mpg.

jimtoo
06-06-2009, 06:09 PM
Hi Dan,

Welcome to the Heartland Owners Forum and hopefully family.

I moved this post to the Towing Area where you should get plenty answers. Myself, I have an 04 GMC 3500 Dually, D/A and pull a Bighorn 3055RL. I gross about 22,500 loaded and ready for the road. I get about 10.5 to 11.0 .

Jim M

gmc
06-06-2009, 06:31 PM
I have an 06 duramax and pull a bh 3055 at about 21,300lbs and average between 9.5 and 11mpg. depends on the terrain

bill40
06-06-2009, 07:51 PM
Hi Dan weclome aboard.
I was getting about what Jim was getting with my 05 (3.73 rear) and the 3500RL. I had the Banks system installed and I know it did help my empty mpg a good bit. Will get a good idea in a week when we leave for a trip. As Butsh said depends on the terrain and which way the wind is blowing, that can be abig deal out west.

Forrest Fetherolf
06-06-2009, 08:03 PM
06 2500HD Duramax 6 spd Allison extended cab, CGVW 22000+ lbs 3600RL Bighorn = 10.5 to 11.5 mpg @ 62 mph 1650 rpm. Summer blend diesel .5 mpg better than winter blend.

Forrest

bigdob24
06-07-2009, 09:15 AM
Thanks for all the info, this is a very good site . I have been looking around and there is everything here when ya look.
Thanks again
Dan

Del600
06-08-2009, 07:57 AM
I have an 06 GMC and tow a Sundance 2998RB, I have yet to get to the scales..... but keeping it under 2000 rpm I see as high as 14mpg, and as low as 10.5.

CrazyScotsman
06-08-2009, 08:09 AM
A lot will depend on what your rear ends are, 3:73 or 4:10's if 4:10 expect lower fuel mileage than the 3:73's

brickman
06-08-2009, 09:39 AM
I have an 04 chev e/c s/b gas that I have never gotten better than 8 mpg towing 7800# conv. trailer. Went to 08 GMC (its a rocket) with this Landmark and get 12.5 towing @ 61 mph, and 20 dry @ 71 & 22 @ 60 mph.

htneighbors
06-08-2009, 11:54 AM
Like others - 10.5 towing the CYCLONE; 20-21 otherwise.

jwb187
06-08-2009, 03:16 PM
An 05 here, just returned from the Smokies, traveled about 900 miles round trip most of it on I-40 across Tennessee. Tried to hold it to around 63-64 mph to keep from getting run over by the thousands of semis on that road!!! I got exactly 11.0 MPG. jwb.

newbie
06-08-2009, 08:31 PM
I have an 04 chev e/c s/b gas that I have never gotten better than 8 mpg towing 7800# conv. trailer. Went to 08 GMC (its a rocket) with this Landmark and get 12.5 towing @ 61 mph, and 20 dry @ 71 & 22 @ 60 mph.


Exact same here. And I take it real easy also. Stay 60-65 regardless of higher posted speeds (when towing:rolleyes:)

yondering
06-08-2009, 09:07 PM
New to this forum, I, also, have a '06 3500,duramax,6 spd allison, pulling an '09 3580RL Bighorn.about 24,000 gross weight. On our last long trip,feb 09>april 09, we towed 9,860 miles, and averaged 12.8 round trip, from Texas to northern California and return. only improvments I have done are K-N Filter system and Bully Dog turbo back exhaust. Good luck, and God Bless ya. Al Weaver, Marshall, Tx

porthole
06-12-2009, 08:07 PM
I have done a couple of changes to my truck and recently averaged 13.5 for 1800 miles, about a 1/3 of that in the mountains of western NC, GA and TN. That is up from 11.5 previous.

This is with my motorcycle trailer which is a lot lighter then my trailer. But I regularly cruise at 70-75 with it when I can.

Something I just heard about but have not tried yet is towing in 5th (with the tow mode engaged).
This will have the engine run at a slightly higher speed but not work as hard.
Food for thought.

Duane

itsbeertime
06-13-2009, 12:49 PM
I *used* to get approx 11.5 according to the trip computer. I recently upgraded my OEM 245 tires to 265's and according to the trip computer I have lost 1.5 to 2 mpg. Not sure how that works, but it sure stinks.

ct0218
06-13-2009, 02:31 PM
With the Duramax/Allison combination you cannot change the computer to compensate for the size change. GM cannot do it, and many dealerships will not even work on the truck if your problem relates to drivtrain or mileage problems. That said, putting a larger tire on would make you believe that with the larger circumference you would get slightly better MPG--but, the opposite happens. It has been discussed many, many times on different forums that the additional mass and weight actually reduces your MPG, and changes your rear ratio to a numerically lower number. That means that it will hurt your towing because your ratio changes from 3.73 to something in the 3.5X to 3.6X range. Even though the tires look small on the GM 2500/3500 series they are the right size for MPG and power through 2006 or 2007 model years. At that point thet did change the Allison and Duramax computers for a slightly larger tire and wheel. Unfortunately, none of that is backwards compatible for those of us with the older models. The newer trucks do not get as good mileage as the older do even though they have a 2nd overdrive, possibly due to the size change, and definitely due to the DPF.

JohnDar
06-13-2009, 07:55 PM
With my '09, I got about 11 mpg when I towed our BH up here to Indian River. At that time, it only had about 3000 miles on it and I kept it to 65 mph. Driving up here today, without the trailer, I was getting 18.4 mpg until I hit the hills north of West Branch. Then it dropped to 17.0. I was cruising at 75 mph. Truck only has about 4200 miles on it so far, so it is far from being broken in.

ct0218
06-13-2009, 08:07 PM
I have heard many say 20K miles for the breakin, and whatever mileage you get at that point is it. I have 148K on mine now and has been consistant for a long time. Changing the speed from 65 to 70 drops my mileage about 1.5 to 2 MPG.

Bob&Patty
06-13-2009, 11:06 PM
Clark, could you clear something up for me please. You say in your post that if I change tire size that I can not reprogram the trucks computors. Also can you tell me who has said this. Was it a Chevy dealer or someone on a forum. Dont want to start a fight here, but I work as a Chevy tech. When I changed tire size to the 265's, I installed the GM scan tool and reprogramed mine. My speedo is right on the money, trans shifts at the right shift points, and my ABS works as designed. Thanks in advance for your input on this issue. Bob:D

ct0218
06-15-2009, 10:05 PM
Bob
It is possible that since the 2008 (?) MY went to 265/75 tire sizes that it allowed that size to be programmed in prior MY GM trucks. I know that until recently the only size tires that could be programmed in was the 215/85, or the 245/75, which is almost exactly the same circumference. I haven't checked recently since they went to the slightly larger tire and wheel. Most guys went much larger size and that did not work. My neighbor has had several 2003-2005 GMC trucks and neither local dealer was able to change the tire size when he purchased them. The dealer installed larger tires/wheels but never could get the change to take. I remember reading many threads on www.thedieselplace.com (http://www.thedieselplace.com) over the years where the size was changed but as I remember only 1 or 2 aftermarket programmers, like EFI or Edge, would actually change the size in the computer. I haven't kept up with this lately since I have no intention of changing sizes, and I know that going any larger with my truck will affect my towing, but there should be a lot of threads on that forum addressing that size change problem. Like I said, if the larger size currently in use has allowed it to be retrofitted to prior model years, then that is good for those doing it.

Bob&Patty
06-15-2009, 10:30 PM
Clark, what I know for a fact is that any GM truck can be programmed up to and including a 33" tire. I have not checked on the the new body style's yet, but will ask about them. Just to clear something up though, any module (computor) that is replaced in a GM car or truck "has to be programmed to that vehicle". It is done over GM's tech line using the OBD11 and CANDI MODULE (after 2006) scan tool hooked up to a computor in the tech's work area. Some of the newer ones, are hooked up the same way and also hooked to a phone line (PITA). This is a direct link to the GM data base. Confussed yet? There might be a possibility that the shops that people have gone to do not have someone that can do the reprogram, wont do it for free, or just wont do it. I hope you understand what I was saying in my previous post. Not picking on you or anyone else. Sometimes I think people are miss-informed. I dont know about you, but anymore I have got to the point that I dont even believe what I see with my own eyes. Just lots of bad information out there. Bob:D

ct0218
06-15-2009, 11:57 PM
Doesn't that just reprogram the ECM and not the TCM? At least, that is what I understood. You work with it, I don't, but I was with my neighbor after dropping off his truck and that is what both dealers were telling him. There must have been 50 threads on this also, so few must be aware of it being possible. And that is entirely possible considering all the misinformation on the injector replacements.

itsbeertime
06-16-2009, 11:06 AM
Thanks for the replies on reprogramming the computer after changing tires. I specifically asked my dealer BEFORE I did it if they could/would reprogram it and they said no problem. One tech swore up and down you couldn't do it (he's ALWAYS an old grump), but the tech who actually did the work *claims* he reprogrammed the computer for the new 265's. Now, there is no way for me to know if he *actually* did or not and they may have been telling me they did just to keep me happy. It would be nice to know for sure though. I guess I'll always be wondering. :(

porthole
06-16-2009, 11:23 AM
Use a GPS.

Set the truck trip odometer, reset the GPS trip and compare mileage at 100 GPS miles.

as long as you have a relatively clear sky for the GPS antenna your mileage will be very accurate.

itsbeertime
06-16-2009, 12:49 PM
Use a GPS.

Set the truck trip odometer, reset the GPS trip and compare mileage at 100 GPS miles.

as long as you have a relatively clear sky for the GPS antenna your mileage will be very accurate.
Thanks for that tip. I've been putting off getting another toy (read GPS), but there's another reason. :)

Bob&Patty
06-16-2009, 11:43 PM
Clark, when I get a chance, I will make a copy of the procedures for the reprogramming. That should clear up any questions about what is done. Hey BEER, easier yet. Get on the interstate, set your cruise at 60 MPH, set your trip meter to zero, drive for 1 minute and check your readings. BOB:D:D

itsbeertime
06-17-2009, 08:32 AM
Clark, when I get a chance, I will make a copy of the procedures for the reprogramming. That should clear up any questions about what is done. Hey BEER, easier yet. Get on the interstate, set your cruise at 60 MPH, set your trip meter to zero, drive for 1 minute and check your readings. BOB:D:D
@Bob: I'd love to see a copy of the procedures. That way I can walk in there and ask to be shown that they did it.

@Bob: 60 on the Interstate??? HAHAHA! I'd get run over and killed. :rolleyes: Hmm, maybe I can find a side street though...:D

NWTFHunter
06-17-2009, 12:11 PM
I have a 2006 GMC 2500 Duramax/Allison and tow a Bighorn 3055. Had everything weighed upon arrival at the Rally last week. Truck & trailer = 20,175 lbs. I got my best mileage ever on this trip, 13.0-13.2. Most of the route was interstate and I drove 58-60 mph. I have a new set of Goodyear tires on the BH and sure if they helped or not. My milage prior to them was about 11.5-12.

ct0218
06-17-2009, 08:56 PM
Bob, thanks--I would appreciate that. Some dealerships are just impossible to work with, and do everything they can not to help you. I got all my injectors replaced, no questions, no charge, in 1 day. The neighbor I spoke of had a GMC that was worse than mine, they replace 1 injector after 4 months of denying that it was defective, and charged him a deductible. It was in the shop for 10 days. He visited my NC home the following month, and got them all done at the dealership I used, for the same no-charge as I did. Nothing changed with the truck, it was bad injectors the whole time, yet the Tallahassee dealership gave him the runaround and overcharged him. They tried to charge him to replace the 7 that they wouldn't change under warranty, and stated that GM had denied the claim. The Asheville dealership said "no problem"
and replaced the 7. So, as you can see I believe a lot of things I have heard was impossible may actually be possible, you just have to show them in black and white. Some techs are poorly trained, some are just lazy.

Bob&Patty
06-17-2009, 09:17 PM
Clark and Beer, your welcome. Yes Clark i know what you are saying. Maybe thats why some of the dealers are being closed down. Gives a bad image of GM. Not with standing, the dealer I work for will bend over backwards to help. As soon as I can get a copy of the procedure's, I will figure out how the post them on here. Fair enough? Bob:D

ct0218
06-17-2009, 10:00 PM
:D Sounds good to me.

Dmaxcc6spd
07-30-2009, 11:30 AM
We just did about 1300 miles from near Cincinnati, OH to Charleston, SC. We averaged 14.15 mpg for that trip. The mods are: K&N stock replacement filter, Kennedy Diesel ECM and 4" exhaust, 265 tires with ECM reprogrammed to match. I had trouble staying under 70mph. My truck likes to run 65-70 on the interstate. This trip also included I-40 and the Jelico mountain climb. I didn't downshift much on the way to SC, but did more of it on the trip back. Seems to like climbing hills without OD and I let the engine rpm sit at about 2500.

I couldn't be more pleased (well a bigger fuel tank would be nice!)

R.Pratt
08-14-2009, 09:48 AM
i have the lmm 08 cc sb with a 3850 cyclone
driving from lakeview oh to enterprise al holding 70 i was pulling around 8.5
dropping to 60 got me 9.0 empty freeway i pull around 20 - 22
just have to watch out for the famous "regen" cycle

PUG
08-14-2009, 11:40 AM
02 duramax boosted to 305 hp (+75) pulling 3950 at 18,500 lbs. Get 9 to 12 depending on hills.

Chainsaw
08-16-2009, 10:26 PM
I *used* to get approx 11.5 according to the trip computer. I recently upgraded my OEM 245 tires to 265's and according to the trip computer I have lost 1.5 to 2 mpg. Not sure how that works, but it sure stinks.

did you have your computer changed when you changed the oem tires? It takes about 2 minutes to do. I had the same problem when I changed tires and went up.

ChopperBill
08-17-2009, 02:14 AM
did you have your computer changed when you changed the oem tires? It takes about 2 minutes to do. I had the same problem when I changed tires and went up.
I had the dealer change the setting on the computer to 265's and it made no difference on the speedo. Found out later that all it does is make the ABS work in conjunction with the 265's. Installed the Edge w/Attitude and it will reprogram the speedo.