I have a 2002 2500HD GMC 4X4, extend cab, short box, with the Duramax/Allison. I have a little over 33,000 miles. I don't seem to get the kind of mileage I see posted on many/most of the RV Forums. I get around 16.5 to 17.5 driving around town with a little of highway -- which seems to be about what others report. On the highway I rarely break 20 mpg. I drive the truck around 70 mph on the highway when empty. I recently did a 3 week trip towing our Nash 23-5A 5th-wheel trailer from Colorado to several destinations in Texas. I've never weighed the trailer but the gross dry weight is listed at 6620 lbs, so I suspect I'm towing around 8000 to 8500 lbs. Pretty light compared to what others are towing with this truck. I did well to get 11 mpg! Two tanks were 9.2 and 9.4 mpg towing in really strong headwinds. Most of the time I got 10.6/10.8 or so. Absolute best was 14 with a really strong tailwind.


At what speeds are you folks towing? I usually tow around 64-65 mph - about 1900 rpm. I leave the tranny OUT of tow haul and run in 5th most of the time, with shifts to fourth on the hills. If it gets hilly I take it out of cruise and drive off the foot so I can let the rig slow down a bit more and keep the tranny in 5th most of the time. Would it be better to wind the duramax up more - run in 4th more (Tow Haul?) - or running at a higher speed -- or slower?


Thanks

I don't think that is too far out of line.


I get a little better empty and towing mileage but I live in flatland at 550 ft above sea level in Ohio.


We I towed my 30 ft Trail-Lite TT 6100 lbs gross to Hilton Head SC through the App. Mountains, I got about 12.3 going down south at about 60-65 and 11.7 mpg coming back north at about 65-70 mph.


I tow @ 80 lbs. all around and do not tow in T/H mode.


To be honest, I would like to know how these guys are towing big weight trailers and getting better mileage.


I think that the problem is those of us with large frontal area trailers, (like camping trailers) will get lower mileage than those towing car-haulers or low profile trailers. The Dmax is real sensitive to wind load.

70 psi in the tires


7425 pound load + 5 people, 3 pitbulls and all the junk for our vacation.


18 mours of solid driving from ND to ID going over the rockies.


65 mph 90% f the time but rolled up to 75 a couple times.


15.6 mpg on the way over and 13.8 on the return trip (went a bit faster on the way back)

AK Duramax mirrors what I am getting. Three adults plus dog, 8500 lb travel trailer (Cougar) and 900 lbs tongue weight. 58psi in the tire (have the 285's on it with max of 65psi). no big trips with the DMax yet, but pulled to Mammoth Caves from Chattanooga two weeks ago in the driving rain. Going up was 12 mpg at about 60 to 63 mph. Coming back, sunny and warm in the 70's, ran 65 to 68 mph and got 13. wife said it was because we were going south. One big hill coming and going, Monteagle with 5% climb and descent.


Pulled mountain and never had to go over 15psi boost and temps in the 700 egt. truck pulled strong and long with plenty of power left over. about 60 mph on the long pulls (4 miles) but felt I could have run it harder with no problem.


Trailer tires are at max inflation.

Anybody pulling a 5th-wheel? I wonder if that "air trap" created by the fiver overhanging the bed might have anything to do with it. Last spring my wife and I were towing into Las Vegas in a really strong wind and I looked back and noticed that the plastic milk crate that I carry my chock blocks in was inverted and floating under the fiver. I had lost most of my plastic chocks. Wonder if thats indicative of the air flows under the fiver? I also tow with my tailgate in place and wonder if a flow-thru tailgate might help. I'll also check my trailer tire inflation pressure more closely.


Jim

I average 11mpg just towing a 5000 lb trailer; I expected better

Pulling 12k on I-81/I-40 through hills of TN, I got 9-10 MPG.

Recent trip from Las Vegas, NV to Mississippi I averaged 9.8MPG for the entire trip. I was pulling a 36' 5er which is 15,300lbs on the CAT scale. Just me in the truck. The mileage went all the way down to 7MPG for one tank in New Mexico when we had a real strong headwing and lots of mountains. Best was 11.8MPG with a tailwind and flat land. I drive 5MPH over the speed limit while on the interstate. I have 265 BFG AT TA's filled to max press. Empty I average 17MPG +- 1.5MPG.

Looks like I just better be happy with what I'm getting and not sweat the small stuff!! I'm going to be taking a trip to Oregon in a month or so, and I'm going to check inflation pressure in the trailer tires (probably max them out) and I might remove the tailgate just to see if that helps. I also may play around some with cruise versus no cruise. Thanks for your replies.

jimandkarla


When pulling even a slight grade I take it off cruise to allow the truck to loose a few MPH. If you leave it on cruise it trys to keep you at the set MPH and will downshift early and often. I also always tow in the tow\haul mode, this is the only way the Allison will auto grade brake which makes one heck of a difference even in a panic stop. I also know what you mean about the "airtrap" in the bed. It took me loosing a garden hose to realize how much turbulence is back there when towing. Don't know how much you will gain by removing the tailgate as the air will just back up on the front of the 5er (underneath the front cap). Don't know, maybe it'll help though.

neverenuff - I also tend to take it out of cruise on the grades unless they are pretty slight and I think I can pull it without shifting. I only use tow/haul when going down steeper grades - for the grade braking. With my light trailer, the grade braking is often too much and it really slows me down - even on pretty steep grades! Are you towing in tow/haul pretty much all the time? If so, what kind of rpm are you turning just cruising down the highway?

I get about 10-10.5 mpg when pulling our 5'ver. I drive 65 mph with the cruise on in tow/haul and the engine is turnning about 2000 rpm's. When going up the hills, it will downshift and hit 3000 rpm's. Within 2-3 seconds, it will upshift and turn about 2700 rpm's. When it reaches the top or flattens out, it will upshift again and drop the rpm's back to 2000.

I get about 10-10.5 mpg when pulling our 5'ver. I drive 65 mph with the cruise on in tow/haul and the engine is turnning about 2000 rpm's. When going up the hills, it will downshift and hit 3000 rpm's. Within 2-3 seconds, it will upshift and turn about 2700 rpm's. When it reaches the top or flattens out, it will upshift again and drop the rpm's back to 2000.


DOn't even pretend there are hills in this state...lol. Giving you a hard time.


I tow in tow/haul mode. the largest milage difference for me is speed. If I go 60 I will get great mileage but all the cars get pissed at the slow mover....I just stick with 65 and give them the finger.

The hills I was talking about were the Black Hills in South Dakota. Tow/Haul worked as advertised going down them.


Wait until you get over into the Red River Valley. The elevation difference there is less than 1 foot per mile in most places. Hard to get water to run off the fields.Edited by: Darin Billing

Like most I haven't weighed current set-up! 5ver is rated for max weight of 10,000 lbs and I keep alot of stuff in it. I run with Tow/Haul engaged. Run 65 psi in all tires. Speed is 65 - 68 mph per GPS (Speedo is off by 2mph). The Jayco 5ver has alot of frontal area. Best towing mileage was last fall, Sundance, Wy to Mitchell, SD @ 13.89 mpg towing the Jayco 5ver and a utility trailer w/ATVs on board. Worst was last week running from Chamberlain, SD - Rapid City, SD @ 6.51 mpg w/etremely strong headwinds (did I say headwinds)pulling the same load. But it maintained speed and was able to accelerate when needed. Usually I am in the high 10s to high 11s per my spread sheet. Empty I get anywhere from just under 20 to just under 21 mpg. One time I broke 21 mpg running 55 mph in the U.P.Edited by: Runaway

I can't find the scale ticket, but as I recall our TT weighs a fuzz less than 7000 loaded for camping.

I've only made three runs with the DMAX pulling this trailer. MPG has been between 10.5 and 13 in each case. I always use tow/haul mode, unless I forget after a stop, but put it in T/H as soon as I notice.

The three runs were:

1) Arvada - Jackson reservoir. About 65 or 70 miles. Truck was barely broken in enough to tow. 10.5 MPG

2) Arvada - Dillion Reservoir. About 75 miles up and over the continental divide on I-70. Truck was more broken in but still under 10k. 13 MPG

3) Arvada - Raton. About 230 miles down I-25 through Raton Pass. Approaching 10k on truck. 12 MPG

Generally speaking I run the posted speed limit but don't spend much time at 75 MPH (the posted speed limit in rural areas of Colorado) when towing. Usually I keep it between 70 and 73 for a top speed in these areas.

Grade breaking kept me at or just below the posted speed limit coming down the grades (occasional break application) on the Dillion Reservoir and Raton trips. DMAX kept me going up them at the posted speed limit though I did see down shifts to 4th on the steeper grades.

I have seen 19.7 MPG unloaded on the interstates running the posted speed limit (mixed between 65 and 75). I believe I could break 20 MPG if I stayed at 65 or lower.

The truck this DMAX replaced was an `02 F-250 CC SB 4x4 with the V-10, 4R100 tranny and 3.73 gears. That gas guzzler would get 6 MPG towing the same trailer across Kansas, and would struggle to maintain the posted speed limit.

The DMAX is an `03 2500HD CC SB D/A 4x4, completely stock.

-Gary

Edit -- I run the front tires at 55 and rears at 70 with the trailer tires at 50 (max for the trailer tires). I still have the OEM Bridgestone 245/75R16s on the truck.


Edit -- I'm not sure where my head was, but now that I've done some real towing (Denver to the Virginia coast), my mileage is 10 - 11 MPG towing. On further consideration I realized that the 12 and 13 MPG I reported above was mixed driving (some towing, some running around in the campsite area). Sorry for the bougus data.Edited by: gary

I'm surprised at the number of people running in tow/haul all the time - even on the flat! I'll check it again, but seems to me like I'm running about 1900 rpm at 65 mph with tow/haul off. Seems like it really runs the rpm's up if I hold it in tow/haul. I'll give it a try next time.


Jim

Make sure you are just pushing the button in and releasing right away. If you push it in and hold it for about 2 seconds, you are turning the OD off. With the OD off, you will see higher RPM's.

Darin - That's exactly what I seem to be seeing. It feels like I turn OD off when I just quickly punch the tow/haul button. Is there a difference between 2002 & 2003? I'll pull out my book this afternoon and see what it says


Thanks


Jim

I pull a 13.5k tahoe transport 33TB usually with a vette in it. 12' 8" high and a very steep front. I averaged just barely over 10 on my last trip to So cal and back from Southern Idaho. Lot's O hills. I do 65 on the 2 lanes where I can and try to stay about 68 on the interstate.


80 psi in rear 70 psi in front, 80 psi for the trailer tires, 2240 on the pin with 40 lbs in the firestone bags.


Forgot: I always use Tow Haul to keep the tranny running a bit cooler (HMO) becasue of torque convertor lock up.Edited by: turbospl311

JimandKarla





I always pull in tow/haul. Don't really remember what my RPM's are while towing.

I just bought an '04 Duramax/Allsion. I have not towed with it yet. The Allison transmission has an Overdrive Lockout and a Tow Haul mode. I planned to use TH as I did with my prior truck (00 Chev 6.0L gas), but I am not sure what to do about the OD lockout. What trans setting(s) are people using while towing? I usually will be towing in the SE USA and not have steep, long climbs or descents.


Anyone here switch to a Duramax/Allison after a gasser? I used to tow with a 2000 6.0 L Chevy 2500 with AT and a 4.1 rear end. I always used TH when towing. It was my understanding that the TH mode only affected the shift points; it did NOT lock the tranny out of OD. I averaged right at 10 MPG towing 58-60 MPH.


If you switchd from a gas to diesel tow, what differences or peculiarities have you noticed? I was concerned with the diesels lack of engine breaking - how's that work with the Duramax/Allison?

Paper





You need to post these questions in the main forum. You will get plent of responces there, no one will see it stuck in someone elses thread.

PaperSniper,


When towing with the D/A combo, unless your GCVW is over 16,500 lbs, you won't see any benefit from using the T/H mode as per GM. However, I do use it for grade braking while going down mountains.


In respect with the OD lock out, I doubt that you will also see much benefit with using it unless you call lower Fuel milage a benefit.


I'm not sure of the weight of your Forest River, but I'm guessing around 7500?


As far as your last question, the grade braking feature is active in either mode. It's just more pronounced in the T/H mode.


You're going to notice a tremendous difference in towing ability coming from a gasser to Diesel. I certainly did. http://www.dieselplace.com/forum/smileys/Big Smile.gifEdited by: DavesDmax

Thanks Dave. The Wildcat I'm towing probably weighs 9000-9500 equiped for a longish trip. I'm not sure what my combined weight is as I've not gotten the truck's (factory) weight yet, but I'm guessing it must be around 7000? That could give me a weight close to the 16.5 you mentioned.


With my previous 6L Chev 2500 gasser (loved that truck!), I used to always use the T/H mode when towing, it seemed to give me better acceleration and power while getting up to speed. With the new D/A, sounds like I will still be using it, but now for the gradient braking more than the acceleration. http://www.dieselplace.com/forum/smileys/Big Smile.gif


I don't see why I'd mess with the OD lockout mode.


What are the gauges you mention in your signature line? "..not installed yet.....:

I am currently on a trip from Idaho to New Mexico. I pulled most of the trip down two lane (US 6, 191, etc to Santa Fe). In a head wind, the computer said 8.5 MPG for the first tank (typical Idaho head wind in the Spring). I did not reset, and when I got to Santa Fe, the computer had an average of 10.5 MPG. Oh yea, pulling a 36 ft Cameo 3-slider, figuring the loaded weight at 13K. Towed all the way in T/H mode and at an average speed of 65-75. I let 'er shift up in criuse to keep speed at 65-70, so did not try to keep RPM down. I was happy with these numbers. My 454 with the same trailer was a 5-6 mpg experience. http://www.dieselplace.com/forum/smileys/Disapprove.gif
I will pull back more Interstate back up through Denver, so will see if a difference.
Also, I was very happy with the performance. First long haul, and I lost count of the 30 plus foot 5'ers pulled by Furds, that I blew by. Maybe Furd owners have a light foot, but they all were pullin' hard, and the Dmax, well she was greathttp://www.dieselplace.com/forum/smileys/Big Smile.gif

i only use tow haul mode when climbing steep stuff. i pull a 24ft 5th wheel and drive about 65 and 70 and have gotten on average 12.5 but i've only had it out 3 times.
back and forth to work i get about 16 to 17 and running empty on the freeway i get @21 i've got about 47,000 on the motor and it is dead stock. looking at an afe air intake.

What are the gauges you mention in your signature line? "..not installed yet.....:





Turbocharger boost pressure and Exhaust Gas Temp, (EGT) gauges.


I just have to get time to drill tap mount cut splice, etc. I got everything to do it, just trying to get courage. http://www.dieselplace.com/forum/smileys/Embarrased.gif

My Sunnybrook FW weighs right at 8500# ready to go down the road.


My last trip, Albuquerque to Ft. Collins and back. 11.36 on the way up, 11.53 on the way back! I run with the "Juice" on level two or three. Set the cruise control on 70, sit back and listen to whatever radio station happens to suit my fancy. I click down to 65 to go over Raton Pass! I DID NOT shift out of overdrive the entire trip going up. I believe a little Juice will pick you up about 1 MPG simply because you stay in Overdrive more.


Winds were light on this trip. As mentioned above, these high profile FWs are a detriment to good mileage. I've seen as low as 8.5 towing into 30 mph headwinds.

GWMAYES - Off topic (but since I started this mess, maybe I can get away with it) Tell me about your 27RKFS. I really like the look of the floorplan, but I can't find a trailer to look at. The dealer here in Denver doesn't have a 27RKFS nor do they plan to get one in the future! How has the unit held up; any problems; what's your general impression of the Sunnybrook? The floorplan is very similar to the Arctic Fox 27-5L which we like a lot, but the Sunnybrook is lighter due to the aluminum frame I suspect. Do you have ample storage in the basement? Laundry chute(opening) into the basement? I believe the tanks are heated - how do they heat them - off the furnace or electric heat pads?


Thanks Jim

I pull 6000 flat with what ya'll would consider an ancient truck and get 14mpg @ 70. To the guy that wants to take the tailgate off or put a flow thru on, Texas Tech did a wind tunnel study some years ago and determined you will get worse mileage without the push of the solid tailgate being up.

I pulled a 28' Carver Sport Cruiser (boat) it was around 12,500lb and the trailer was around 1k so total of 13500..i got 9-10mpg..depending on the speed..actually pulled it pretty good....But yea..the wind defintley affects the mpg...

When i pull any other boat usualy around 6-8k lbs i average 12-13mpg...

I have a 4000# camper and tow a 4200#boat and trailer. I go to Lake Naciemiento in central Ca. from LA area. numeous times a year, I get 9.6 to10.6 mpg going 70-75 mph. I tow in T/H for the braking and higher shift points. I use cruise but take it out at the bottom of the hill. If the hill is long and steep I like to take it out of OD so it isn't shifting back and forth. I expected better milage but compared to the 454's I've had well need I say more?

Now this is "no s--t" (doesn't everybody fib about their milage) My GCVW with half a tank of fuel, wife and dog at the time I weighed was 21,623 (I have the ticket) and I was getting 10.3 mpg. at 70 mph. Solo maybe 17 average. It has been as high as 19 solo.

I don't care what it gets as long as it tows with ease so I can listen to some tunes and play with my road toys. (GPS, CB, attitude monitor and scratch my fanny)
Denny

Brand new out of the box towing(I know, old truck died on trip) a 17ft. Vnose about 4500# the truck got 10.5 from Texas to Maryland. Now with 13.6K it gets 14.5 towing the same trailer and load. The truck dosen't even know it's towing. All around empty is 16-17, stright highway 19-20. My old gasser got 6.5 to 8.5 towing, don't miss it at all.

Recently completed a 7k trip out through Yellowstone, Moab UT, Durango CO, Santa Fe NM then home. Lot of miles in the Rockies. Pulling our 35', 102" wide 11' 10" high 5th wheel we found the mileage ran between 10 and 13 mpg--truck had about 28k on it. We weighed at start of trip and found a GCVW of 21,460#. :eek: Based on our axle wieghts we kept front tires at 55 psi, back at 80 psi and trailer at 80 psi. We typically drove 60-65 when speed limit allowed.

Grade braking got a real good test going down one long winding 10% grade in Wyoming and it worked great.:D

On a trip east through West Virginia to the Virginia coast last year we averaged between 11 and 13 mpg (was before we added the auxillary fuel tank). Best we ever got without trailer was a little over 21 mpg driving 65 on relitively flat Interstate in Michgan.