I am in Texas now after a 1600 mile trip from Wisconsin. I have an '03 Duramax crew cab with a camper shell. I am pulling a 27' Jayco TT weighing about 6000lbs. Here is my fuel economy so far. Will update when I get home. Please comment.

Avg for total trip....Going 60-65mph. 10.98mpg
Avg at 60 mph .............................. 12.52mpg
Avg at 65 mph .............................. 10.43mpg
Best mpg, going 60mph with favorable winds
and flat grade................................ 13.7mpg
Worst, headwind, hilly dropped to 4th gear a lot
.................................................. 9.6mpg

Thanks for any comments. This is our first long trip with the camper. I titled this "LIARS" because everyone down here with a Duramax (there are a LOT in Texas) SAY they get 13-15mpg pulling their giant fifth wheels. I say Bull, but maybe mine is a fuel sucker. BTW, I calculate by miles divided by fuel, no DIC info. SPICER

Milage is a lot like **** size: I think everyone is a little optimistic. :)

I know my truck doesn't get the mileage a lot of people say, and neither does my dad's '01. For that matter, neither does our Stroker.

I titled this "LIARS" because everyone down here with a Duramax (there are a LOT in Texas) SAY they get 13-15mpg pulling their giant fifth wheels. SPICER
Now come on Spicer, not all of us have claimed great numbers on the MPG. I've always said that I get between 8-8.5 with my worst being 7.5.

Have you had that trailer wieghed? No offense, but 6000#'s seems a little light.

TT

I would expect you to do slightly better. My trailer is a bit longer and heavier and my numbers are a bit better at those speeds. Could you have been on Winter fuel most of the way? Wind resistance seems to be the biggest factor, even over weight. The best towing mileage I’ve ever gotten is 14.12 between Grand Junction and Dillon (I think it was Dillon), Colorado on I-70 at 65 mph whenever the truck would hold it. That is definitely not flat ground, but we had a ferocious tail wind virtually all the way. The next best was 12.1 across southern Idaho running in calm air at 65 on flat ground. The rest of the time it’s in the 9-11.5 mpg range, but I usually tow in the mountains. Since adding the Juice at level 1 the mileage has improved about 1 mpg, or so. It’s always a question whether someone is giving real fuel mileage numbers of **** size, but there seems to be a fairly consistent trend suggesting that fifth wheels are a bit more aerodynamic than TTs. Maybe the lack of a big gap between truck and trailer smooths the airflow. My truck is a DIC-less wonder and mileage is always hand calculated.

TC

My truck is a DIC-less wonder and mileage is always hand calculated. ):h

MPG's are a funny thing, never consistent, hard to nail down, etc. There are so many variables that go into MPG's it is highly unlikely we'll ever see real consistency. Factors to consider are: tire pressures(all) and size(yes size matters); frontal mass(T/V and trailer); headwind; hills/mountains; humidity; driving style; traffic; weight; mo' weight! ):h

See where I'm heading with this. IIRC the best DP MPG calculated at around 12 towing on flat surface here in Florida, worst was 7. Spicer, you might consider a tow tune of some sort, EGT gauge, and a higher flow exhaust. IIRC the guys that are posting the higher MPG's are all running these applications. Good luck! JJ :)

MPG's are a funny thing, never consistent, hard to nail down, etc. There are so many variables that go into MPG's it is highly unlikely we'll ever see real consistency. Factors to consider are: tire pressures(all) and size(yes size matters); frontal mass(T/V and trailer); headwind; hills/mountains; humidity; driving style; traffic; weight; mo' weight! ):h
:exactly: Now thats clear, concise, and accurate :exactly:

Or, as O'Rielly would say.....Pithy

My mileage is pretty consistent with Spicer when pulling a load.

I think that MPG is related to DNA. My DNA for example tows at 10 MPG. Intl 9670 with a 14L Detroit got 10 MPG towing loaded. The C5500 gets 10 towing, the C3500 got 10 towing, the K2500 got 10 towing, and the C1500 1/2 (a dually heavy half) got 10 towing. The biggest difference was time.

Others seem to have different DNA that allows them up to twice that, and there is no other rational explanation for it, since these folks always tell the truth, and have the check in the mail to prove it!

What I want to know is how to "hand calculate" a "DIC-less wonder" (we called it something else in the Navy), would'nt you need a "DIC" to "hand calculate :confused: .

RF

Spicer,

Your mileage is about the same as mine. I might get a little better on flat land. I attribute any mpg difference between your rig and mine strictly due to the aerodynamics of our respective trailers.

Mine is a 30ft Trail-lite with an enclosed underbelly and a sweptback frontal area. Weighs about the same.

I achieved the same results towing to Hilton Head, SC

My best is 9.5 pulling and my worst in a 30mph head wind was 7.5.

I sold a supercharged/intercooled 8.1 Suburban that got a best of 7.8 MPG while towing (run 13.9 at the track). I though I would be picking up at least 4-5 MPG by getting into a Duramax. I guess I was reading stories from the people that get the big MPG with their 5th wheels. My first towing trip last week gave me mileage in the 9-11 range. Not really close to what I was expecting. Even my father in law tells me stories of getting mid teens while towing the same size trailer (20-24' enclosed car hauler). I'm hoping my new "V" nose trailer will break the wind a little better and help with mileage.

if you use the search, you will find other threads that give good ideas to raise mileage, its all been said many times, we pull 63 ton total with our detroit and are close to some of your mileages

Tbyrne,

Even though you didn't get the big number improvement in mileage, as a percentage of your original best a bump from 7.8 to 9-11 mpg is significant. As your engine loosens up it may go up a bit more.

TC

11 MPG is a 50% increase so that isn't bad when you look at it that way but I expected more like 1.75 over what I was seeing from the Suburban. I just read a thread in the Performance section (http://dieselplace.com/forum/showthread.php?t=27721 that recommended having the Edge's low boost setting at 1 for good fuel economy. They were talking about power level 3 with 1 for low boost. I wonder if this would be helpful while towing. I think I have mine set at level 4 or 5.

I have just the Juice w/o the 'Tude. I can't mix and match the tuning levels so I tow in plain old level 1. I have seen a mileage improvement. It's not huge, and I need to put some more towing miles on to get a true reading, but it looks like another 1 mpg, possibly a tad more. Nowadays every little bit helps.

TC

My C4500, when towing 10,000 # of loaded Airstream, travelling at 70 mph, managed 7.8 mpg, on a stretch with long uphill sections, and 8.3 on the flat. when traffic kept me down to 60 mpg, I got 10.6 mpg.... I will tow at that speed if possible, in future. I will be getting a larger trailer, sometime this year, and will see how to keep the 10+ mpg with that... Probably will not do it though.

I was getting 18.7 to 19.2 on trips with bare truck stock with stock tries. I went to 265 and drop to 16.7 to 17.3. Did not tow any with stock tries. Towing the trailer in my sig. I went out west to Washington and avg. 9.7 over all tow 65 to 70 on interstate. This fall I went to Tenn and the Smokies I avg. 10.5.
I talk to a gentelman with an 05 2500 and he said he was not getting over 6.9 pulling a smaller 5er than mine. Or the 05 worst on miliage?

Mylash,

Many tow-behind trailers (even the slick airstream) create more drag than a fiver because the nose & cab breaks the wind for the trailer, hence some fivers can get the same fuel mileage, often better, than the tag-along folks.

You won't know till you try. I get 10.x average with an 8,100 lbs fiver + 7k lbs car on dolly (tandem) on the east coast with the heavier C5500 @ 65mph (4.44 - LRWD).

RF

I am in Texas now after a 1600 mile trip from Wisconsin. I have an '03 Duramax crew cab with a camper shell. I am pulling a 27' Jayco TT weighing about 6000lbs. Here is my fuel economy so far. Will update when I get home. Please comment.

Avg for total trip....Going 60-65mph. 10.98mpg
Avg at 60 mph .............................. 12.52mpg
Avg at 65 mph .............................. 10.43mpg
Best mpg, going 60mph with favorable winds
and flat grade................................ 13.7mpg
Worst, headwind, hilly dropped to 4th gear a lot
.................................................. 9.6mpg

Thanks for any comments. This is our first long trip with the camper. I titled this "LIARS" because everyone down here with a Duramax (there are a LOT in Texas) SAY they get 13-15mpg pulling their giant fifth wheels. I say Bull, but maybe mine is a fuel sucker. BTW, I calculate by miles divided by fuel, no DIC info. SPICER
The final tally now for the RETURN trip, 1610 miles
Total return trip avg..................12.21mpg
Avg at 60 mph.........................12.35mpg
Avg at 65 mph.........................11.5mpg
Best, 60 mph strong tailwind.......13.92mpg
worst, 60 mph, some wind..........10.38mpg

Total average for trip, 11.59mpg
Total avg at 65 mph... 10.71 mpg
Total avg at 60 mph....12.39mpg.
....This was a 27' Jayco Jayflight Bunk House TT.

So about 1.7 mpg better at 60 mph vs. 65 mph. So at 65 mph I would burn 298.77 gallons over 3200 miles. At 60 mph I would burn 258.27 gallons, for a fuel savings of 40.5 gallons or about $90. Numbers are fun! SPICER

That's about what I found out too.

If I keep my speed under 62mph, my milage will stay pretty decent.

I remember some posts along time ago that said the Dmax sweet spot is around 61-62 mph. and around 1850-1900 Rpms.

These trucks are just like horses, if you want them to work harder, feed them more...

Don't you just love these MPG's posts? :D

"tbyrne: They were talking about power level 3 with 1 for low boost. I wonder if this would be helpful while towing. I think I have mine set at level 4 or 5."

tbyrne, I hope your not saying you are towing in level 4 or 5? If so, unless one of your mods so far is a Suncoast III, TTS or equivalent tranny upgrade you might damage the tranny! :eek: Wazzup? :)

Spicer, those are respectable towing numbers, especially without any programs or upgraded exhaust. IIRC the guys towing with higher MPG numbers are running programs and upgraded/modified exhaust. I just had the MBRP 4" cool duals put on, E/J w/attitude ready as well. ;) I'll know more when I have a chance to strap my 5ver on in a couple of weeks. Will advise. :)

Lest we forget we're getting more HP/TQ from these engines stock than ever before. Comparing them to the old 6.2's, 6.5's and 7.3 PSD's and others isn't "comparing apples to apples". We have an enormous amount of hp/tq under the pedal, even more with mods. Five years ago guys were complaining about 8-10 mpg's with their diesels when towing over 12k lbs+- trying to go 60-70mph. :o: Now we want to yank those weights and more at 70-80mph and get 12,13,14+++ mpg's. :rolleyes: Are we ever happy? ):h

There appears to be a lesson with Spicer's results. Those that back off the pedal will likely notice an increase in their MPG's, both for towing and not towing. Apparently the diesel engines produce so much low end torque they appear to not operate quite as efficiently at higher RPM's, say above 2200. If MPG's are your game then slow down. The speed demons out there that push the higher RPM's, it may not be too realistic to expect high MPG's. :cool:

Good discussion! JJ :)

Guess I have no complaints . Last summers trip to Nova Scotia pulling '76 ,25ft airstream , 5000# ,average 14.2 pulling ,60-65 highway. 1800 mi. round trip , hand calc for Canadian and liters.

.

Don't you just love these MPG's posts? :D

Lest we forget we're getting more HP/TQ from these engines stock than ever before. Comparing them to the old 6.2's, 6.5's and 7.3 PSD's and others isn't "comparing apples to apples". We have an enormous amount of hp/tq under the pedal, even more with mods. Five years ago guys were complaining about 8-10 mpg's with their diesels when towing over 12k lbs+- trying to go 60-70mph. :o: Now we want to yank those weights and more at 70-80mph and get 12,13,14+++ mpg's. :rolleyes: Are we ever happy? ):h

Good discussion! JJ :)True, but when you look at what Class 8 tractors get pulling loads that dwarf what we do, it kinda leaves one scratching your head... as long as we're compairing apples and oranges. :D

When I worked for PACCAR and the KW T2000 came out, IIRC they were claiming an avg. of around 6 mpg. Now how much can that thing pull at that rate compared to me at 10k# getting 8-9? I suppose most of it comes down to the fact that we don't have enough gears available to always keep the engine in the most efficient RPM range.

"I suppose most of it comes down to the fact that we don't have enough gears available to always keep the engine in the most efficient RPM range."

Oilbrnr, I think you nailed that one on the head dude! Give me 10-15 gears and watch me rip! ):h JJ :)

Yes JJ. a good-ol' Eaton Fuller 9-speed would have been an option I wish I had (except that they are not synchronized = double-clutching).

Never seemed to want for power in my '89 COE 9670. With only 210 Hp / 900 lb.ft. Tq from the Detroit, and weights up to 80K, I could manage 55-60 all day long, even with only roughly 300 Rpms to work with.

Now you make me feel that I should of sprung for the C6500 instead. I guess its my turn to start sweet-talking my co-driver on the next truck!

RF

Having Mama JJ on my heels is enough for me! :o: I don't need Mama RF3 stalking me to! :eek: Please leave ol' JJ's name out of this one! ):h JJ :)

Spicer,

My numbers are real close to yours. Last June, took a trip from Bismarck to Austin, Texas with the 5'ver. The 5'ver weighs about 10,000 lbs fully loaded.

On the trip, the worst was 9.2 mpg with about a 40 mph head wind. The best was 11.9 mpg (DIC showed 12.6) with one tank reaching 16.3(about 1/2 of that tank was without the camper). Down and back, overall was 11.089 mpg with the DIC showing 11.3. That was a total of 4022 miles with about 400 of those miles where I wasn't pulling the 5'ver.

All towing was with the cruise set at 65 mph in tow/haul.

I feel better with these "honest" numbers. I suppose at 55 mph I could see the numbers these exagerators see. I was very diligent with my speed. One tank at 60 mph, the next at 65, etc. I just got 19.5 unloaded on the highway going 65. I'm happy!. SPICER

Now with fuel prices going through the roof, many of us may determine that pulling at 55mph isn't such a bad idea.

If prices get to $3.00 a gallon or higher, going a little slower may pay for the refreshments for the trip.

when i pull my jayco fivr, i see in the 10's and 11's mostly...sometimes in the 12's

I averaged 8-9mpg on a 1000 mile trip last week with a 40' 5er weighing over 15k lbs. This trip also went thru the Blue Ridge Mountains and the Smokey's. I also got my injectors replaced that trip.

mileage is a funny thing, although I didn't tow over Easter I went to Clarksville TN. On the trip down I got 18.4, driving around down there and back, 19.6 with my final tank showing 18.8. The last week Feb I went to FL and average 16-17 the whole trip. Why such a variance? Don't really know.

Rick, I see numbers that seem inconsistent also. I think the main variables in mpg come from speed, terrain (hills and grades) and wind/drag. If you have a 20 mph headwind and are going 60mph, the wind drag is equivalent to 80 mph. Your mileage is still better than if you were going 80 mph though because your rpm's are less. But wind drag is exagerated with a big camper. I got drastically different numbers going the same speed with tailwind vs. headwind. Seems like basic logic. The other variable is filling the tank. I always try to fill the tank all the way up to be consistent every tank, but the amount of foam can vary a lot. So sometimes I may have the tank full and other times I may stop filling due to foam and still be a gallon from full. This messes up the mpg calculations a lot. over the long haul the average of the numbers will be really close. SPICER

I kind of think that first gear is too low anyways, and changing the rears from 3.73's to something like 3.42 or 3.31 may help lower rpm's in 5th. The gear spacing in the allison I believe is OK. I kind of feel the same way about my surburban, '97 K1500, 350 gas. 1st gear is too low, and the gear spacing between the gears is too large for pulling heavy loads, and the engine gets out of the power band when going up hills. GM needs to take their 4 spd auto, and make the gear spacing closer, with 1st gear not as low. I don't think GM has these trucks geared optimally.

With the Dmax/Allison, does anybody think that 1st gear is not low enough with the 3.73 rears, and if so, under what application?


BTW, I get about 15.5 mpg empty, and with pulling a 26" car trailer, about 8500 lbs, I got about 12 mpg. Truck is stock.

SPICER
I was thinking, if the discussion was about engine RPM's vs. MPH. We would be able to compare the different setups that people are running. By increasing my tire size from stock, I have been able to increase my ground speed and keep the RPM's down allowing me to get better mileage on flat terrain. On the flip side the larger tires have changed the way I have to run hills when loaded.

ffrrules
If I could have the use of the 6th gear that is already in the allison I would want 4:10's. Getting the weight rolling when your GCVW is 28K+ can be a challenge even on a small inclines. I don't race, so the need to drive 95+ mph just isn't there. Being able to haul loads at hiway speeds +10% without the rpm's being to high would still be nice.

Arlen next time you take that camper out for a tow let me know and I'll let you borrow my juice to try. I run stock most of the time except for tow haul in traffic areas like Chicago where the extra power for passing and acceleration are needed. It'd be interesting to see how much it helps out on towing capabilities and economy if any.

RVC, 28K is a lot of weight. Is there some kind of legal limit you can haul (GCVW) with a 3500? I had just assumed it was up to 24K, ? hydraulic brakes. I thought over 24K you needed air?

Anyways, I would think 1st gear needs to be low enough to get the maximum weight rolling on a reasonable incline. Making 1st too low will make the gear spread between the other gears wider, harder to continue to accelerate up an incline. To me , overdrive should be geared such that you would be at optimum rpm's at about 65-70 mph, ?1800 rpm's, mainly to use when you're empty, cruising, or hauling on level ground. The gear spacing in between 1st and 5th therefore needs to be spaced to keep the engine in its optimum powerband, with the gear spacing narrowing somewhat as you go up through the gears. My suburban is definitely not geared like this. The GM engineers must have been smokin something when they designed the gear ratios in my tranny. 1st gear is too low, making the gear spread between 2nd, 3rd, and OD too wide, and my truck poops after shifting from 2nd to 3rd.

When your not hauling anything, the gear spacing doesn't matter.

Going to larger diameter tires can definitely lower your cruising rpm's, but you lose braking effectiveness. I learned the hard way at age 16 with my dad's F250, 35" monster mudders.

I mean to say 1st gear should be low enough to start and pull a maximum load up an incline such as a relativeley steep driveway. You don't need a creeper gear with an auto tranny.

ffrrules
I have never been able to get a straight answer about weight and types of brakes, maybe I just haven't asked the question right. So long as the load does not exceed the axle/brake rating, I feel the public and my family are safe with what were hauling.

I think the gear ratio on the current allison is fine I just hope that when the 6th gear becomes available that there is the option to get 4:10's from the factory. If 4.10's are not available the need for taller tires to compensate is another option. Adding a taller gear with the existing 3.73 ratio would make it so that the 6th gear would never be used when hauling as the rpm's would fall below the available powerband.

I think you would be supprised at how many people are running at or around the 28K mark. (6-8K trucks, 7-19K 5th wheels, 5-8K flat decks + load)

The 1 ton car haulers running the tri-axle wedge trailers have to be 28K alot of the time, and are still running electric brakes.
8K truck + 7K trailer + 13K (6K 2cars, 7K 1 truck) = 28K

RVC, 28K is a lot of weight. Is there some kind of legal limit you can haul (GCVW) with a 3500? I had just assumed it was up to 24K, ? hydraulic brakes. I thought over 24K you needed air?

Anyways, I would think 1st gear needs to be low enough to get the maximum weight rolling on a reasonable incline. Making 1st too low will make the gear spread between the other gears wider, harder to continue to accelerate up an incline. To me , overdrive should be geared such that you would be at optimum rpm's at about 65-70 mph, ?1800 rpm's, mainly to use when you're empty, cruising, or hauling on level ground. The gear spacing in between 1st and 5th therefore needs to be spaced to keep the engine in its optimum powerband, with the gear spacing narrowing somewhat as you go up through the gears. My suburban is definitely not geared like this. The GM engineers must have been smokin something when they designed the gear ratios in my tranny. 1st gear is too low, making the gear spread between 2nd, 3rd, and OD too wide, and my truck poops after shifting from 2nd to 3rd.

When your not hauling anything, the gear spacing doesn't matter.

Going to larger diameter tires can definitely lower your cruising rpm's, but you lose braking effectiveness. I learned the hard way at age 16 with my dad's F250, 35" monster mudders.

Arlen next time you take that camper out for a tow let me know and I'll let you borrow my juice to try. I run stock most of the time except for tow haul in traffic areas like Chicago where the extra power for passing and acceleration are needed. It'd be interesting to see how much it helps out on towing capabilities and economy if any.
I have heard some say mpg goes up with a chip. If I believed this was true and that it would cause no harm I would probably look into it. Most get juice for speed. I'm just not into that. I can see it. I get a chip for mpg, try it on a higher level and become an adrenaline junky! Is that how it happens? SPICER

So RVC,

let me ask you this. When starting out with a 28K weight, with your power adders turned off/down, does your truck struggle in first gear? Have you started out at the bottom of a hill? Do you think your truck needs to be geared down more in first?

I would say that pulling 28K is a true test for proper gearing. If your truck easily pulls in first, then you should be fine with larger diameter tires, but again your braking may suffer some.

Power is like an addictive drug but you need to know your limits. Although I own a Predator and a Juice I'm almost always running stock. Why you ask? Because I'm more than pleased with the power that a stock Duramax has to offer, and in all honesty I'm still a polite driver that allow people in merging traffic and seldom am I running late for where I really need to be. The power is fun to play with, but not something I need on my daily commute, I'm just not that important where I need to be everywhere NOW!

ffrrules
I run with the edge on level 2, throttle response 4, defuel on all locked shift. When starting with a 28K GCVW, I would be able to tell you weather the road is angled up, down, or level.

I'm very happy with the way that the truck gets the load moving even when starting at the bottom of a hill, which is what I face every time I haul hay.

I also happy with the way that the truck is geared. I just hope that when the 6th gear (dbl OD) is available in 2006, that it won't be a running empty crusing only gear. I have had my anti-lock brakes adjusted for the tires that I'm running, I don't care if the speedo is off by 4%, I don't think it was accurate with the stock tires.

SPICER
I can confirm the use of the juice has improved my milage both empty and hauling. To date I have had no abnormal engine/transmission issues because of the juice. That is with 90K on an LB7 and 26K on an LLY. You would actually be one of the people that could enjoy the milage improvement, as you say your not interested in becoming an adrenaline junky. I have to admit playing around once in a while can be fun.