Chevy / Duramax MPG?

[JBlomenberg]

Haven't posted in a while, but came across something I thought I'd pick your brains about.



First, my 2001 Dodge/Cummins 2500 2wd Auto usually averaged about 21mpg for interstate driving between 70 and 75mph. My new to me 04. 5 is getting more like 17-18 at the same speed. But, that's not my question.



I've had a conversation with someone that claims that their factory stock 2005 Chevy 2500 4x4 gets 30+ MPG at interstate speeds between 65 and 70 mph. They've done the math, calculating the MPG as well as relying on the on-board computer.



So, yeah, I'm a bit sceptical. Especially since I work for Cummins as an engineer, and have a fair bit of experience in performance development on the larger High Horsepower Engines.



Anyone heard of similar claims out there, and if so, how's the Duramax doing it?? Seems to me that basic physics begin to take over at 55mph +, such as aero drag and other factors, and even if the Duramax was pretty efficient, I can't imagine it is 2x better than the Cummins.

 

[RACE427]

Duramax

There is no way that Duramax is getting 30mpg. I know someone who owned one and saw nothing even close to 30 mpg. Just think about it, if it were getting 30 mpg, GM would have it all over their commercials trying to sell the truck with the Duramax option !!!!

 

[steved]

My coworker has a 2005 Duramax, and he gets at most 15mpg... he has kicked himself for trading his 91 CTD.

 

[JBlomenberg]

Kinda what I was thinking. Expecially with Diesel prices being what they were last year and are now. Chevy could almost rescue GM from impending doom by selling 30mpg HD pickups.



They showed me a picture of their on-board display showing 32. 7 mpg. I can get that in mine too if I idle around the parking lot for a while. :-laf

 

[HBarlow]

Flying J diesel pumps are often populated with Ferd or GM diesel owners who always want to lie to a guy driving a Dodge-Cummins with their ridiculous claims of fantastic fuel mileage. It happens only in their dreams or coasting down a long mountain grade. V8 diesels deliver approximately 2mpg poorer fuel mileage than our Cummns-powered trucks in all conditions.

 

[EKlem]

The biggest factor in mileage for these trucks is wind resistance. 30+ would be possible with the right driver and a truck seriously modded for better airflow but not on a remotely stock shaped truck. There are examples of people with each brand that are in the high 20's with some serious mods and careful driving. But they have put in significant work both to the truck and their driving.

All brands have people who inflate their mileage claims. We are lucky that the dodges have consistently resulted in some of the highest mileage. It is impressive to see some of the numbers that the new LMM trucks are turning in when driven correctly.

 

[abrankod]

Another issue that we face as diesel drivers is being pretty far off the torque peak of the engine at 70-75MPH. Typically for the 5. 9 CR ISBe engines that peak is about 1900RPM. If one were to re-gear the drivetrain to put the engine right smack dab at the torque peak at whatever speed, thats where you'll see the biggest gains in MPG. any more rpm, and you're just "spinnin' your gears" Its one of the reasons that OTR trucks surpass our smaller diesels in mileage while towing. They happily loaf along at their torque peak at a chosen speed. Ever notice how truck drivers tend to settle in at speeds that don't seem like a logical multiple of 5 or whatever... Its because they settle in to a speed where they can make their best mileage at whatever their top (or near top) gear is. I often wish i had a 10 speed RoadRanger with a double overdrive, but alas, they don't make such a fantastic beast... I think that with proper gearing and a good constant speed (hmm I think I heard that in a song once) one could achieve a consistent 3-5mpg gain over the stock configuration which has the engine in the 2200-2300 range while at 70-75mph.

-Dan

 

[BDaugherty]

MPG is half vehicle and half driver. My buddy sold his dad his old Honda Accord when he bought a new one. In several years of driving it, he never made it over 30 MPG. His dad routinely gets 40+MPG.

My '01 2500 4x4 with 2" leveling kit, 35" tires, and 4. 10 gears has been getting 17. 5-18 MPG.

Another buddy had a '03 2500 4x4 Dmax with 3. 73 gears and 285/75 tires. He routinely got 13-15 MPG. Unloaded highway only would get him 16-17.

My old 5500 Dmax would almost get 8MPG... . loaded.

 

[peobryant]

Haven't posted in a while, but came across something I thought I'd pick your brains about.



First, my 2001 Dodge/Cummins 2500 2wd Auto usually averaged about 21mpg for interstate driving between 70 and 75mph. My new to me 04. 5 is getting more like 17-18 at the same speed. But, that's not my question.



I've had a conversation with someone that claims that their factory stock 2005 Chevy 2500 4x4 gets 30+ MPG at interstate speeds between 65 and 70 mph. They've done the math, calculating the MPG as well as relying on the on-board computer.



So, yeah, I'm a bit sceptical. Especially since I work for Cummins as an engineer, and have a fair bit of experience in performance development on the larger High Horsepower Engines.



Anyone heard of similar claims out there, and if so, how's the Duramax doing it?? Seems to me that basic physics begin to take over at 55mph +, such as aero drag and other factors, and even if the Duramax was pretty efficient, I can't imagine it is 2x better than the Cummins.

I think the biggest reason people with the Duramax think they get the best mileage is because of the "Diesel Power Challenge. " On the fuel mileage test a Duramax with some kind of injection (I think it was propane) got around 33mpg (It has been a while since I read the article) while all the others running on fuel only didn't come cloe to that. Seems like a fair test doesn't it?

 

[DCreed]

I wonder If you ran an aux tank of fuel if that would count for mileage in the challenge? That way with a large aux tank you could easily double or triple the miles achievable with the stock tank. just like with propane. cheater! Just like NOS/water/LP/whatever, lets do a "fuel only" power challenge.
and like everybody else here, I too, have heard all the rest stop BS about 30+mpgs of every make as well as 600hp with a "chip". Just smile and nod, uh-huh.

 

[HBarlow]

Another issue that we face as diesel drivers is being pretty far off the torque peak of the engine at 70-75MPH. Typically for the 5. 9 CR ISBe engines that peak is about 1900RPM. If one were to re-gear the drivetrain to put the engine right smack dab at the torque peak at whatever speed, thats where you'll see the biggest gains in MPG. any more rpm, and you're just "spinnin' your gears" Its one of the reasons that OTR trucks surpass our smaller diesels in mileage while towing. They happily loaf along at their torque peak at a chosen speed. Ever notice how truck drivers tend to settle in at speeds that don't seem like a logical multiple of 5 or whatever... Its because they settle in to a speed where they can make their best mileage at whatever their top (or near top) gear is. I often wish i had a 10 speed RoadRanger with a double overdrive, but alas, they don't make such a fantastic beast... I think that with proper gearing and a good constant speed (hmm I think I heard that in a song once) one could achieve a consistent 3-5mpg gain over the stock configuration which has the engine in the 2200-2300 range while at 70-75mph.

-Dan

A Cummins ISB beginning with the 24 valve in 98. 5 does not have a "torque peak" at a specific rpm as you wrote above. The ISB used in our Dodge Rams produces maximum torque from about 1600 rpm to about 2700 rpm. The torque curve shows on a graph as flat, not peaked. The new 6. 7 used in the pickups produces 650 ft. lbs. of torque from 1500 to 2900 rpm in automatic transmission configuration.

You can see graphs of the torque curve of our Cummins ISB engines on the Cummins website and in all the Dodge truck brochures I've seen.

 

[Gaylord]

Duramax vs CTD

I just recently purchased a 2006 GMC with the Duramax/Allison, 3500, Crew Cab, dually. Running empty, combination of freeway/town driving, the best I have experienced is 18. 6 MPG. Oddly the computer showed less (17. 9).

Towing my 27' Holiday Rambler, I experienced 14. 2 MPG.



My '94 signature Dodge routinely gets 21 to 21. 5 MPG running empty and between 13. 0 and 17. 1 towing the above trailer.



In my opinion, the Dodge is a very poor tow vehicle. It was always, except after I purchased a Hensley Hitch, a situation where the tail was wagging the dog. After driving my friend's GMC and experiencing the power and smoothness of the Duramax and the superior Allison Transmission, I purchased the GMC.



I have kept the Dodge for running around empty, as I have my '86 Ford F350, std cab dually. It has a gas guzzling 460 and I no longer license it, but use it as a yard donkey. I could put my HR Trailer on the Ford, sans equalizer or sway controls and it would tow without issue, always and in all conditions.



Remember though, that comparing the Dodge to the GMC is comparing apples to oranges. A 160 HP engine simply will NOT perform like a 360 HP engine. It does however tow without issue, sans the Hensley, the equalizer and sway (friction) controls. I also wanted a crew cab so I could take the grand kids with us. I also wanted a vehicle that would tow without issue. The GMC does just that.



I didn't consider a newer Dodge, based on my experience with the '94. I do wish that the GMC would get the mileage of the Dodge, but the towing issues made the choice easy. I'm not trying to flame anyone, just stating the mileage differences & why I didn't get another Dodge. Of course YMMV.











.

 

[HBarlow]

... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .....
In my opinion, the Dodge is a very poor tow vehicle. ... ... ... ... ... ... ... ... ... .

Remember though, that comparing the Dodge to the GMC is comparing apples to oranges. A 160 HP engine simply will NOT perform like a 360 HP engine... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .

I didn't consider a newer Dodge, based on my experience with the '94. ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ..... /quote]

Each to his own, I guess. No doubt a stock automatic tranmission '94 Dodge with 160 hp, narrow operating band, and the old 47RE with loose torque convertor was not a great tow vehicle. I test drove one at a dealer back in 1994 and rejected it. But as soon as Dodge offered the 24 valve HO engine with manual six speed transmission in 2001 I bought one.

It's interesting that based on your experience with that truck you made the statement that "the Dodge is a very poor tow vehicle. " Which other Dodges have you towed with? You even compared the towing ability of an older Ram 2500 "3/4 ton" with a 3500 GM. Is the GM a dually?

It's too bad you didn't try towing with any 24 valve Cummins and particularly any Gen III Dodge Ram with horsepower and torque figures similar to the GM before you made the decision. You would have experienced the light truck industry's superior tow vehicle.

A Duramax doesn't produce any real towing torque until you wind it above 2500 rpm. That is why GM doesn't even offer the Duramax with a manual transmission any longer and also the reason why the Duramax downshifts on every grade, sometimes down two or even three gears to maintain speed or to keep up with a Dodge-Cummins. Has anyone ever seen a published graph showing the torque output curve of a Duramax? Cummins and Dodge show theirs in every brochure.

When I was transporting trailers I pulled all day with fellow transporters driving GM Duramax trucks pulling similar trailers on several occasions. I could pull the grades in 6th gear in my old 2001 Ram with 3. 55 gears at 1600 - 1800 rpm and the other driver's Duramax/Allison would fall back on every grade until the Allison downshifted to rev the engine up to around 2500 rpm.

Enjoy your GM and keep on believing it is a superior tow vehicle.

 

[AClayton]

I agree with Harvey.....compare the Duramax to a CTD of the same vintage and the ' rules change ' significantly. My brother in law has a Powerstroke in his work van and has to constantly rev the engine to do the same work as my truck pulling more weight. The 94' was also the 1st of the 2nd Gen. vehicles and they didn't get it right with the powertrain at 1st.



Took my family to Disney in Jan. and one of our fellow campers saw that I had a Banks Power sticker on my MH and struck up a conversation with us. He asked me what mileage I was getting and I quoted that I get 8 mpg and have bested at 8. 5 on level ground before. He chuckled and said that Banks makes good products but he re-programmed his computer in his MH himself and boasted that his rig... . a 38'triple-slide with the same chassis and 8. 1L gas engine routinely achieves 15mpg all while towing his Hummer H3. My MH is a double-slide 35' and all I tow is a CRV and could never expect to get over 9mpg empty,let alone pulling a heavy sport-ut like a Hummer. He also started bashing diesels and said that gas engines are coming back as the pullers of choice with both power and mpg. I listened to him until I just couldn't take anymore and my wife and I walked away... . It takes all kinds!!!





Alan

 

[JLEONARD]

That's funny... he couldn't get 15 if had that engine in a pickup let alone a big rig.

 

[HBarlow]

I agree with Harvey.....compare the Duramax to a CTD of the same vintage and the ' rules change ' significantly. My brother in law has a Powerstroke in his work van and has to constantly rev the engine to do the same work as my truck pulling more weight. The 94' was also the 1st of the 2nd Gen. vehicles and they didn't get it right with the powertrain at 1st.

Took my family to Disney in Jan. and one of our fellow campers saw that I had a Banks Power sticker on my MH and struck up a conversation with us. He asked me what mileage I was getting and I quoted that I get 8 mpg and have bested at 8. 5 on level ground before. He chuckled and said that Banks makes good products but he re-programmed his computer in his MH himself and boasted that his rig... . a 38'triple-slide with the same chassis and 8. 1L gas engine routinely achieves 15mpg all while towing his Hummer H3. My MH is a double-slide 35' and all I tow is a CRV and could never expect to get over 9mpg empty,let alone pulling a heavy sport-ut like a Hummer. He also started bashing diesels and said that gas engines are coming back as the pullers of choice with both power and mpg. I listened to him until I just couldn't take anymore and my wife and I walked away... . It takes all kinds!!!

Alan

Was the guy with the 15mpg gas hog big block GM motorhome inside Disneyland wearing his Mickey Mouse suit when he told that ridiculous lie?

I usually tell the fools in the GMs and Ferds who approach me at the Flying J fuel islands "I don't know, I don't ever check it" when they ask about my Dodge's fuel mileage. It's a waste of good air to talk with them. I know when they walk up they are envious of my Dodge and want to tell me some outrageous lie to make themself feel better.

 

[rbattelle]

I've had a conversation with someone that claims that their factory stock 2005 Chevy 2500 4x4 gets 30+ MPG at interstate speeds between 65 and 70 mph. They've done the math, calculating the MPG as well as relying on the on-board computer.

I've always said, most people decide on a fuel economy they're happy with and report that as fact. They're not lying - they have genuinely convinced themselves.



This guy is either failing basic math, or doing something weird with his fillups (such as not refilling completely). Or his coworkers are playing a cruel (but expensive) joke on him by slipping in a couple gallons when he's not looking.



To stop these sort of things cold, I advocate asking the person to see the fuel log. Doesn't have to be mean-spirited, you can tell them that's remarkable and you'd like to have a look at his fuel log.



Almost no one keeps a fuel log.



Ryan

 

[Wiredawg]

A good friend of mine (in his 70s) claims 28 mpg fromm his '99 3500 auto. I had installed 275 injectors and it had a power module adding about 100hp. Running stock tires, 70 mph and 3. 54s 2wd. I sat in the drivers seat and noticed his fuel gauge half full and 300 mi on the tripmeter. My 2000 2500 4x4 6spd 3. 54s would read 300 mi on the tripmeter half full an would translate to roughly 17 to 18 mpg. Just wasn't worth it to bust his bubble or hurt his feelings.



Had a guy at work tell a story about one frineds GMC D-Max/Allison how great it towed and how it left his other friends Dodge behind and how it struggled to keep up. I told him my Dodge could tow his frineds D-Max and trailer better than his friend's D-Max could tow the trailer. I my experience, one BS story deserves a better BS story.



BTW, My avg mileage in my 2000 2500 6sp 4X4 QC was 17. 5, it avgs 13. 5 on my 2002 3500, 18mpg on my '93 and 18 on our 2003. I guess the driver does have somenting to do w/ mileage.



Happy Trails.



Wiredawg

 

[CWebster]

Duramax's average mpg is 13-15 mpg. Some a little more, some a little less, but averaged out its usually around those numbers. I've had several dmaxs and Cummins..... not to mention they build them here in Flint and every swingin bowtie round here has one. Every truck that comes out of that plant (light duty and medium duty) has touched, used, or benefited from products, assemblies, fabrications, or material handling solutions that came from my facility... ..... I choose Dodge/Cummins.



Chris

 

[TFucili]

I agree with Harvey.....compare the Duramax to a CTD of the same vintage and the ' rules change ' significantly. My brother in law has a Powerstroke in his work van and has to constantly rev the engine to do the same work as my truck pulling more weight. The 94' was also the 1st of the 2nd Gen. vehicles and they didn't get it right with the powertrain at 1st.

Took my family to Disney in Jan. and one of our fellow campers saw that I had a Banks Power sticker on my MH and struck up a conversation with us. He asked me what mileage I was getting and I quoted that I get 8 mpg and have bested at 8. 5 on level ground before. He chuckled and said that Banks makes good products but he re-programmed his computer in his MH himself and boasted that his rig... . a 38'triple-slide with the same chassis and 8. 1L gas engine routinely achieves 15mpg all while towing his Hummer H3. My MH is a double-slide 35' and all I tow is a CRV and could never expect to get over 9mpg empty,let alone pulling a heavy sport-ut like a Hummer. He also started bashing diesels and said that gas engines are coming back as the pullers of choice with both power and mpg. I listened to him until I just couldn't take anymore and my wife and I walked away... . It takes all kinds!!!


Alan

My '04 Chevy with 8. 1/Ally got 8MPG pulling a lightly loaded 7'x14' cargo trailer. It never got over 11MPG empty, and was a piece of junk that I ended up going lemon-law on. Must be some good stuff he's smoking! It's sad that people have to dream up such drivel to justify their purchase. Why not be a man, and just have the balls to say you didn't want a diesel, and are willing to pay for gasoline?!