I am new to this site and should be picking up a LLY/Allison 4x4 extended cab 2500hd SB Silverado tomorrow. I picked GM because I have been very happy with with 1995 Sierra and 1996 Chevy van I own. Picked a diesel because close to 75% of my driving is towing a 5000lb travel trailer. I was using a 1995 350 v8 Sierra which averaged 6 mpg towing, and even redlined it had trouble going 45 mph through passes. It was really beating the truck up and I am hoping to get at least 10 mpg towing hopefully better....


My question relates to the fact that no MPG figures are published for HD trucks, and if you asks people what they are getting you seem to get a huge range with diesels. Everything from incredibly high to no better than a gas motor. I have driven a Mercedes non-turbo diesel that my Dad has had since 1983 quite a bit but never really concerned myself with MPG as it is pretty good and has only one acceration rate(SLOW). I don't want to do any modifications and don't have the money anyway. I have been told that diesels have a very critical range for RPM for best fuel economy when towing and am also wondering about the use of tow/haul and OD lock out with a trailer in my weight range? I spent almost 60% of my winter expense hauling the trailer down south on fuel this year. Getting 2-3 better would be really worth it to me. Anybody have any helpful hints on best rpm, highway speed, using the features of the Allison, and driving technique to maximize MPG??? Also wondering why diesel fuel is 30-40 cents a gallon cheaper in the Northern midwest than regular gas but the same price in much of the southwest? Can't wait to get my new truckhttp://www.dieselplace.com/forum/smileys/Big Smile.gif


Thanks,

Hey Sam


Here are my results so far with my truck. It has 3000K miles on it now, and mileage is 15 empty around town, and 12-13 towing my 6000lb enclosed work trailer around town.


The use of the tow haul mode will decrease mileage sustantially IMO. I use it in town with the trailer, and on off ramps. It holds the gears for a much longer period of time, thus increasing RPM'sand fuel usage. The trailer at 5000lbs is not real heavy for these trucks, and the tow haul is kinda over kill 100 % of the time. Its great in stop and go and around town driving, but once up to speed, or on the interstate, its not really needed. Especially if you have a good brake controller.





When I first got the truck I was disappointed with the fuel mileage but then I realized it was from me getting into the throttle so much. Since then I try not to get above 2000-2200 when bobtailing, and mileage went up considerably.


On the highway I try to keep it at the same rpms to help with fuel mileage as well. It seems to help. I have a cab and chassis x cab with 9' utility body 3500 series. It weighs 8500 alone, and gm installs tiny 215 size tires. You will have 245's from what I understand, so you may be able to run a few MPH faster at the same rpm as me.


IMO you will save the cost of the upgrade to the duramax over the 6.0 gas or 8.1 in just a few years if not sooner. I know I am very happy I got the d max over a gasser.


As for why diesel is cheaper, I dont have a clue, but I do enjoy the cost savings. Right now diesel is anywhere from 30-40 cents a gallon less than 87 octane. Even if gas and diesel is the same cost, you will get 2x the fuel milage as a gasser.


Dino


Edited by: urethane dino

Sam,

My recently acquired truck in the same model and engine that you are getting. Here are the results from the first trip with my conventional 24' travel trailer.

The trailer was about 6,800 lbs loaded. The trip started in Phoenix at 1,100' and ended in the White Mtns of Az at 9,300', with a lot of up and down in between, for approx 220 total miles. The hand calculated fuel milage was 10.3 MPG. The truck had 1000 miles at the start of the trip with 55 lbs in the front tires and 60lbs in the rear. Everything about the truck is still stock.

I would guess the fuel milage to be about 12.5 mpg on a level drive with no wind. I am hoping the milage will improve as the truck breaks in.

Based on experimenting during the trip, I think fuel milage would decrease with the tow hual mode set to on. With the light loads you and I are pulling, tow haul is not needed. The primary purpose of the overdrive lockout is to give you a means to gear down from 5th to 4th, and I would do this on the down hills. I am just going to run mostly with the tow hual mode set to off and without the overdrive locked out. The programming for the Allison seems to take care of everything. The tow hual mode is nice in stop and go traffic since it will automatically gear all the way down to 2nd when slowing down. With the tow haul set to off, the trans only automatically gears down to 4th.

Here's the exciting part. I was able to easily maintain 60 to 65 mph on all the hills (6% grades) without any problem. What a great driving truck. It has great steering and tracking, good stability with the trailer, and the brakes are much better than my old 1/2 ton.

My old truck was similar to your GMC. It was a 1997 1/2 K1500 with the 5.7 Vortec. My no wind level milage was 9 mpg with the same trailer. I do not understand why your GMC is so much lower (6 mpg) with a lighter load.

You will love towing with your new Duramax!

Bruce H.

Thanks for the help. I will be happy if I can get 12 mpg towing and am going to really try to go light on the peddle. Going 50 mph on sideroads really doesn't bother me.


My Sierra had the overdrive automatic and I think a 3.73 rear end. It got about 18 mpg empty with the overdrive. You had to stay in 3rd towing and it increased RPM from 1500 to 2500 to go 60 MPH. I did not have a towing package or tow/haul mode transmission. If it had a 5 speed transmission I am sure it would have been fine but a effective 3 spd was just not any good for towing. To mantain 50 mph required redlining the truck through mountain passes. I took to going 35 mph but that was still 3000 rpm.


I am very happy about the rear disc brakes as the drums on the old truck were a problem spot. It was used daily off road and the wheel cylinders were replaced twice due to sticking from the drums not draining water.





My truck deal is done but can't pick it up until Friday. Looking foward to trying it with the trailer.

I just returned from a 3801 mile trip to Canada and back (to California). I averaged 11.8 mpg and we climbed some monster mountains and drove about 65 mph on the flatlands. I used the tow/haul in all of my mountain driving, and I was thrilled with the response. We also bucked some heavy wind and watched the mileage drop. I pulled a 30' Sunnybrook that was over 11,000 lbs.


Good luck

2004 2500HD, ext, SB, 4X4, LLY, picked it up with a full tank at the dealers Sat morning. Put 347Mi on the trip meter, refilled it with 19G of fuel, That works out to 18.26mpg. not bad for the first tank?





JJEdited by: 02B12S

Hey Sam


Where in the U.P. are you?


I deer hunt in Rapid River, also spend a lot of time up there.

John,


Iron River

Second Tank, local roads, 207.2 mi w11.399gal used = 18.15


Heading out this afternoon/Mass pike/NewYork Thruway to Lake George. This will be the first all limited access highway trip. I'm interested in how it will do. Very happy so far, runs GREAT.http://www.dieselplace.com/forum/smileys/Approve.gif


I'm not yet pulling any load..


JJ

My last tank was towing 180 miles @68-70 mph with a 3-4k# trailer and the rest unloaded. 388 miles, and filled up with 23.5 gallons. 16.5 avg mpg and the DIC was accurate within a 10th.


I still have yet to make 500 miles on 1 tank. I have been close, but trailering or a lot of city driving gets in the way usually.

Towing a 24', 8,000lb racecar trailer, driving from Corona Ca to Las Vegas NV and back, 11.2mpg. I drove pretty fast, and the terrain went from 1000' to 4000'+, with many grades. My gasser got about 7mpg on the same trip with 7000lb.


City driving gets me between 14 and 15 unladen, hwy 17-20. Unladen from Corona to Florida (2500mi) at high speed (often over 90mph) netted 17.x, which was my worse hwy mileage. But the engine only had 600mi on it when I started.


IMO, there is no comparison when towing. It's like night and day. For those who don't tow, you're not going to save much going with the diesel.

Truck is stock with 6,400 miles. Last tank was 20.5 mpg empty at avg 38mph in light hills. Towing a 6,500lb trailer was 12.3 for a full tank. Coming from a Ford Expedition, it is a whole new world of stability and power towing on the highway. I can't wait to hook up again!

I just towed 28 ft aruba 28dbs (7000 lbs loaded out) for 1000 miles and averaged right at 9.5 -10 by hand calculation for interstate driving 75mph, towed wonderfully, I did notice that if I towed around 62 mph fuel milage was around 12.5, I now have 2300 miles, used tow haul only in cities on/off ramps, really saw no decrease in mpg with it on, it really helped stop, especially for the yellow lights. good luck!

Finally picked up the truck. I got(according to the DIC) a peak of 23 MPG driving at 50 mph in 5th gear on a 2 lane road on a 40 mile drive. 16-17 MPG driving around small town. Very poor mileage at low speed/ very low rpm on a two track. When engine is cold mileage suffers big time. MPG seems to peak at 1500 rpm in 5th gear when nice and warm. MPG very sensitive to RPM and quick accelleration, much more so that gas engine. I am very happy so far. Taking a longer trip tomorrow where I will test DIC against actually mileage calculations. The amount of power the truck has is incrediable.

Pulling a 5000 pound load at 70 MPH you should get between 12-14 MPG depending on wind conditions. With that load there is no grade you cannot top at 70 MPH, I know, I live in Colorado and pull in the Rockies. Pull on the tow mode. good luck

No need to use tow-haul unless you exceed 75% of the towing capacity of your truck........gives you a little better mileage by not using it.......JB.http://www.dieselplace.com/forum/smileys/Thumbs Up.gif

Best ever with stock tires was 20.7 keeping rpms under 2k. (not towing)

Just returned from a 300 mile (each way) trip to Gettysburg, PA towing a 36' 5th wheel RV weighing approx. 13,500 and got 11.0 MPG going 63 MPH. Around town without the RV it's in the low/mid teens, on the highway in the high teens.

280 miles towing a 21 ft toyhauler, 12.5 mpg with 3300 miles. THis same route with a tail wind my wife got 24.5 empty. I have gotten 22 on a trip earlier in the week, empty. Have been told that it will only get better as it breaks in.....

Just filled up this morning for the weekend. Mileage was 13.7 per gallon. This was just going back and forth to work in town with no trailer. I expected a little better but the truck still has only 400 miles on it. Maybe it will get a little better once it gets broke in some more. It did get close to 12 this past weekend pulled my 24ft enclosed car trailer.

I have an LLY Crew Cab short bed with approximately 2,200 miles on it.

Combined mileage with a lot of freeway: 15.5
DIC reads around 20 mpg constant freeway.

Combined mileage with little or no freeway (grocery store, kids at school, Little League, etc.): 14.5

Trailer towing (26 foot travel trailer):
13.5 mpg if not too much mountain climbing,
11.5 to 12 mpg if climbing mountains is involved.

Basically if you drive like a grandma you'll get good milage. If you drive so you can pass anyone on the interstate like I do your milage will suffer. but who cares fuel is cheap and it's only money you can't take it with you. Besides The whoever gets the best milage thing is just an ego builder anyway. i'd rather drive fast and race from stop light to stop light.