DuraMax mileage

[HOSS]

Bought new in 2008 Chevy HD Dually with Duramax and Allison trans. 2 wheel drive. Pulls the BH 3670rl great but on the last outing in Nov. I averaged only 8.2 mpg on a 300 mile one way trip. After arriving back home took truck in for service at dealer where truck was bought. They said that air filter needed changing, I thought too soon because truck only has 10,000 miles on it. But I have noticed a 2 mile per gal. gain in around town driving. Hoping to see better hwy mileage when we take BH back out this spring. Showing an average of 13.4 mpg around town driving since filter changed. I like to keep everything OEM and dealer serviced, that way if problem arises there is no question about if "you had not done this, this would not have happened and we are not responsible" kind of situation. That is just my take on it.

 

[DMitch]

My 08 dually is completely stock. I get 14-15 around town. On the highway the best is 17 and towing my 3580 back and forth to Florida average is 10. I have heard many claims of 20 mpg from the LMM's but I don't belive a word of it. On the other hand my son in law has an 07 LBZ and I have been on long trips with him and have seen for myself 19-20MPG hand calculated. Point is you can't compare the different Duramax engines.

 

[wonka]

I would like to say the LML is great on fuel, but so far it isnt, no towing yet, but only running 14 around town. Makes me miss my LB7, 2003 crew cab 4x4, 8200# travel trailer, deck with two 500cc Honda quads, generator etc. rolling down the road at 18000+#'s and getting 15-17 pulling western Canadain Rockies. Lots of gripers when your rig pulls good fuel numbers ( empty the old girl would pull 22-25 mpg's based on foot position). The switch to ULSD hurt the mileage until I started running stanedyne and added a superchips programmer set to tow mode. It doesn't seem to matter what year the duramax is there are sippers and guzzlers, but I find running the additive makes a difference. The tuner worked to increase mileage for me, at least on tow mode (performance was a hoot to play on, but was hard on the fuel consumption). I only have 2000 miles on the new truck, but so far the mileage is improving every tank(only three so far).

 

[porthole]

I am getting 13 miles per gallon in town and 17 on the highway with no 5th wheel hooked up. I expected a couple of miles per gallon better than this but have little diesel experience so don’t know. The air filter was dirty and I am thinking of replacing it with a K&N. Is this mileage typical and does anyone know what I can expect pulling a 3250 (which we will pick up next week).

My 2006 Duramax got about 13-14 around town and 15-17 on the highway.
After doing some post warranty work - 4" exhaust from the turbo back, tuner, air intake with a cold air ram and some other stuff I got the same mileage. The only change from all that work was a slightly quieter exhaust (wasn't expecting that) and a bit of fun on level 6.
Towing – when I was doing 65 I got around 8-8.5. Slowing down to 53-55 I got around 12.
Forget the K&N for the reason mentioned above.
And an FYI on the factory Duramax intake – testing proved it flowed better than any intake on the aftermarket. And filtration was superior.

I use T/H mode whenever I am towing. I did not know that this was providing me with an extra 100HP. Wow!

It doesn’t.
And for that matter if you took a ride in your truck blindfolded and with earplugs with the factory intake and any of the aftermarket intakes you would not be able to tell the difference.

As far as the K-N filter system...save your money. They have a terrible dirt stopping record.

Agree

My best advise is to leave your truck the way it came from GM. All the hype about better mileage from tuner's is a bunch of crap (now the arguing starts).

After doing what I did to my truck I would agree with this too.

All tuner's do is dump more fuel for more power. So do the math...if you dump more fuel your mileage will go down

That is not so. Although using a tuner will allow more fuel it doesn’t necessarily mean you will burn more fuel per mile. Diesels work differently. More fuel and you get more work out of the engine – so you end up using less fuel to get the same work without the tuner.

You also can damage the engine because of too much combustion pressure and heat.

The better tuners have safeguards built in to prevent this. Typical is monitoring the EGT, engine and coolant temps (plus others). Start exceeding set values and the tuners will start “defueling”

BTW, the Duramax's computer will up the HP by 100HP by itself when in Tow/haul depending on the throttle angle

OK – now I raise the BS flag.

In T/H the D/A locks the torque converter starting in 2nd gear. Keeps it locked when you take your foot off the peddle and keeps it locked as the trans downshifts (until 2nd gear). That is why the D/A combo works so great on hills. The PCM also changes the shift pattern, raising the up shift and downshift speeds. Having the converter locked earlier and the shift speeds raised allows the trans to run a little cooler. But mostly it keeps the engine working in the ideal torque range.

 

[caissiel]

With the 6.2L the power would drop after just 5K and the K & N was the solution. So after the first oil change with the 6.5L I checked the filter and and it was starting to grey and through it away and used K & N for 150K and washing it a few times when it got dirty. I drove around home most of the time and was just fed up with the power lose I was getting with those cheap paper filters.

My tuner has been great on my Ford and I tow on all the settings, When I beat on it the fuel milage still is much better because of the torque gain with same fuel milage. Setting on level 1 can give me an increase of 20% torque while towing and the mileage stays the same. On Setting level 2 can give me more torque but better mileage at higher speed like above 2000 RPM that the 6.0l is awfull on fuel above 2000RPM when stock. On level 3, I find the fuel mileage is great at high RPM with torque that is further incresed. I never use the full power available but use the extra torque to give me better fuel mileage at lower Boost.

When my truck is stock, it has no power or torque to stay on cruise while towing my trailer up hill. At every small hill the torque goes up to 100% with just a light increse of accelerator pressure. With level 1, I can increse the torque proportionaly untill 100% at full trottle. I can do the same hill on overdrive with the trottle down to 80% and keeping speeds, compared to 100% stock and loosing speed.

This truck can take all the load I push it through and in no way I get any alarming EGT or water temperaturers.

But with Turbo engines I don't realy think a change of air and exhaust system gives any increse in power or MPG worth the cost of the system. But there is worth while payback in using the Hypertech Econ at both levels A or B, same as my Max Energy Levls 1 or 2. And the Programer can be paid for by using the ScangaugeII for mileage training and savings on fuel that we will be paying over $4 per Gallons.

If any thing the Scangauge and Training ourselves to drive properly can save on fuel mileage, is what I have found is the greatest if scared to use a programer. Without a calibrated Scangauge there is no way anyone can see the values of different OEM settings, Programer efficiencies and bad fuel qualities that are at different fuel stops.

 

[Birchwood]

My 07 3500 GMC dually diesel gets 11mpg towing and 19 mpg unloaded hwy.These are Canadian figures.
This truck has no additives to the power train as I believe GM knows more about their truck
than I.Don't even have a chrome tip on the tail pipe as I feel it will probably rust out the original.

 

[Bob&Patty]

Duane, you say that some of my statements are BS. Well ok, thats your opinion. But as a GM tech for over 47 years and talking directly with the GM engineers. The statements are from the horses (GM's) mouth. Their statement is "up to 100 HP as needed" The HP boost is added by the ECM as needed by throttle angle, trans gear selection and other parameter's. About your "red flag BS" well mine goes into convertor lock up in 6th gear when in T/H mode. As to feeling it...well you might or might not. I do notice that the turbo spools up when it's pulling hard in 6th gear and the RPM's are dropping on hills. All I know for sure is that, it pulls just fine stock and does what I want it to. Sorry, but I have to disagree with you but we can still be friends.

 

[caissiel]

I was looking at the GM 2007 Duramax curves and in order to gain 100HP with the torque locked at 2000 RPM the engine has to produce rear wheel torque off 810Ftlbs.
Hard to beleive it can do that without a programer of some kind. And max engine breaking rear wheel torque is 740 at 2400 RPM.
But I do understand that it will produce 100 HP more at Max torque at 3000 RPM. Which the T/H would shift the tranny to produce it.

 

[porthole]

Duane, you say that some of my statements are BS. Well ok, thats your opinion. But as a GM tech for over 47 years and talking directly with the GM engineers. The statements are from the horses (GM's) mouth. Their statement is "up to 100 HP as needed" The HP boost is added by the ECM as needed by throttle angle, trans gear selection and other parameter's

Bob to clarify – it is said with tongue in cheek, and only referring to the extra 100 HP comment. Just as if we were sitting around a campfire and you told me your truck runs 9.5’s in the quarter.

ASE Certified general category since 78, 18+ years as Chrysler tech and also certified in Mack, Detroit, Cat and Cummins (pre electronics)

“Feeling it” referred to a “seat of the pants” blind test to the various intakes, with claims of up to 40 horsepower. I should have separated that from the other sentence. I think we both agree most of the intake claims are hog wash and that GM supplies the best intake out there.

I know you got time in with GM, but we are referring to the LBZ and higher Dmax’s, which are the best to come out of Moraine. Dmax history is only 11 years old (let’s leave out GM’s former foray into the diesel market J) and the LBZ on up only 5 years old (original poster’s 08, your 07 and my 06).

….well mine goes into convertor lock up in 6th gear when in T/H mode. As to feeling it...well you might or might not. I do notice that the turbo spools up when it's pulling hard in 6th gear and the RPM's are dropping on hills.

Not sure what you are referring to with the L/U in 6th. My point with T/H was that when activated it locks the converter in 2nd gear and keeps it locked all the way up to 6th and back down (although it will unlock if for some reason the trans does not downshift when needed).

Once in 6th the converter locks anyway, tow mode or not. But non T/H it will unlock when backing off the throttle in 6th. That is what makes for a “smooth” transition from throttle to no throttle (think manual trans here). But leaving it in T/H is what give you maximum” cruise grade braking”.

They do work great stock, although a shift kit certainly helps. One of the caveats of early lockup is a drop of line pressure in the trans, exactly when you need the pressure most, under a load.

Throttle angle - I am guessing you are referring to throttle position – as determined by the TPS, since throttle blades are not used.

Bottom line is that at least with the 06 and up Dmax - stock is probably best for the engine. I would still add a shift kit, deep pan and deep diff cover though.

I have to disagree with you but we can still be friends.

Friends –you bet - show me the 100 HP increase and I’ll even buy you dinner and beverage.

 

[Bob&Patty]

Duane, your on...It's in one of GM's internal bulletins but when I was still working at the dealer we could call "TAC" ( technical assistance center) and ask questions. I will see if I can get one of the managers to get me a copy and I will post it or fax it to you. Throttle angle (old school) or TPS...to me..same thing. You never know maybe Ford has the same thing...might be worth looking into. Didn't mean to take offense...but sometimes the written word does not come across the same way as talking face to face. All is well now.

As to T/H you can lock out convertor lockup in all the gears if you want. All you have to do is hold in the T/H button for 2 seconds. The "circle D" lite will illuminate on the cluster when OD is locked out.

Well I stayed up until last year. Went through all the electronic crap until then. PITA. The old pre-electronic stuff worked just fine. A computor to run a power window or seat........GIVE ME A BREAK. Do you remember the 1st power seats, windows and antenna's. 2 were hydrolic and 1 was vacumn. They worked great unless you sprang a leak. What a mess that was. Customer, "I have oil running out of my door" or "I have oil running on my carpet and my shoes are filling with oil". Even better, customer," my windows and seat are not working", tech,"let me check your oil". WHAT???? Electric windows and seats are much better.

 

[TedS]

Sorry, I got lost in the paragraph about tow/haul lock out converter lockup. Are you saying that if I disengage overdrive that the torque converter will not lockup in any gear?

 

[Mike & Carol]

I have a 2009 GMC 2500HD crew cab....empty and keeping speed at 55 on cruise for 75 mile(my normal comute) I consistantly get 23-24 MPG.....thats not how i drive all the time.........my only tow with new Grand Canyon bringing it home 5 hour trip at 55 on cruise I averaged around 13-14+ MPG When I experimented with speed I dropped 2 MPG for every 5 mph increase.
Its all about the SPEED. After all I am on vacation I am not in a hurry......and its so much more relaxing and less stressful at 55.

 

[jimtoo]

Well I stayed up until last year. Went through all the electronic crap until then. PITA. The old pre-electronic stuff worked just fine. A computor to run a power window or seat........GIVE ME A BREAK. Do you remember the 1st power seats, windows and antenna's. 2 were hydrolic and 1 was vacumn. They worked great unless you sprang a leak. What a mess that was. Customer, "I have oil running out of my door" or "I have oil running on my carpet and my shoes are filling with oil". Even better, customer," my windows and seat are not working", tech,"let me check your oil". WHAT???? Electric windows and seats are much better.

Hey Bob... I agree with you on the electronic stuff... computers for windows,, seats...you name it..YUCK!!. ,,, BUT,,, you are really showing your age on the rest of it...

 

[rustyshakelford]

I have a 2009 GMC 2500HD crew cab....empty and keeping speed at 55 on cruise for 75 mile(my normal comute) I consistantly get 23-24 MPG.....thats not how i drive all the time.........my only tow with new Grand Canyon bringing it home 5 hour trip at 55 on cruise I averaged around 13-14+ MPG When I experimented with speed I dropped 2 MPG for every 5 mph increase.
Its all about the SPEED. After all I am on vacation I am not in a hurry......and its so much more relaxing and less stressful at 55.

When I'm pulling the cyclone, I drive at 65. That's right where it will go into 6th gear. Any slower and it stays in 5th with much higher rpms. So far ive only towed about 2000 miles and get 10-11. I use tow/haul. I also test drove a new dodge dually and plan on getting one of the new H.O. Cummins. I'm worried that the mileage will stink!

Brett

 

[porthole]

Duane, your on...It's in one of GM's internal bulletins but when I was still working at the dealer we could call "TAC" ( technical assistance center) and ask questions. I will see if I can get one of the managers to get me a copy and I will post it or fax it to you. Throttle angle (old school) or TPS...to me..same thing. You never know maybe Ford has the same thing...might be worth looking into. Didn't mean to take offense...but sometimes the written word does not come across the same way as talking face to face. All is well now.

As to T/H you can lock out convertor lockup in all the gears if you want. All you have to do is hold in the T/H button for 2 seconds. The "circle D" lite will illuminate on the cluster when OD is locked out.

Well I stayed up until last year. Went through all the electronic crap until then. PITA. The old pre-electronic stuff worked just fine. A computor to run a power window or seat........GIVE ME A BREAK. Do you remember the 1st power seats, windows and antenna's. 2 were hydrolic and 1 was vacumn. They worked great unless you sprang a leak. What a mess that was. Customer, "I have oil running out of my door" or "I have oil running on my carpet and my shoes are filling with oil". Even better, customer," my windows and seat are not working", tech,"let me check your oil". WHAT???? Electric windows and seats are much better.

Well I can honestly say I don’t remember if I ever remembered about hydraulic door locks and seats.
Once I got out of trade school I worked at a small station up in the mountains where there were a few “well to doers”.
We worked on all kinds of crazy stuff. Some old (domestics) – some pricey (few Ferraris & Lambos) some just not destined to run right (MG’s Renaults etc)
Being a MOPAR fan my favorite being the old Chrysler Fire Power Hemi’s. Worked on quite a few on the “monster motors”.

I mentioned the “throttle blade – TPS” as many here may not know the difference, or that most diesels lack a blade.
Actually, I think the new Ford actually has a throttle blade, but it is obviously not for fuel as one would first think.

I don’t recall being able to lock out the TC on my 06. But I doubt I would have anyway. When the lock up converters came out I was a huge fan of them (except the myriad of shudder problems that came with them). With the diesel I don’t see a reason to not use lock up, but maybe some vehicles don’t keep the RPM’s up high enough.

You mentioned T/H and OD in the same reference, is that a slip?
Locking out the OD I can see.

I finally let all my certs expire. Last time I went for renew I missed one of the modules by 2-3 questions. Not bad I figured since I had been pretty much out of the game for 10 years by then. I challenged the test but ASE had no interest in my concerns – so I let them all drop. Don’t need it anyway with my current career. They lose the 150 re-cert money and I save it.

Everything on my new truck is controlled by a PCM, ECM or BCM……………..

 

[porthole]

When I'm pulling the cyclone, I drive at 65. That's right where it will go into 6th gear. Any slower and it stays in 5th with much higher rpms. So far ive only towed about 2000 miles and get 10-11. I use tow/haul. I also test drove a new dodge dually and plan on getting one of the new H.O. Cummins. I'm worried that the mileage will stink!

Brett

If your stuck in 5th at 55-60 take it out of T/H, let up on the throttle a bit and it will shift into 6th.

 

[Bob&Patty]

Duane, the throttle blade (plate) should be just for air intake I would think. GM still uses throttle plates (blades) on most of its cars. Well at least our 07 Chevy Eqinox does.

No, what I was talking about was the fact that you can lock out the torque convertor clutch by holding the T/H button in for 2 seconds. I will have to try it both ways, I never tried it when driving with the T/H off, but I know it works when in T/H mode. Your right about "why would you want to". Well there are stupid people that have NO clue as to what they are driving. ie "I bought a diesel because they are cool". They try to pull a 6% grade towing and just hold the throttle to the floor, yes it will downshift but it wont keep jumping from lockup to 6th direct and burn up the clutches in the convertor. Do you get my drift? Easier to explain in person..I hate typing. Off the subject, I had the the 07 towed out of a snow bank. Another long story for later. The wheels kept locking up slightly when pulling it. HUMM, why did it do that...had it in neutral. So I asked our trans guy..."whats up with that"? Well I guess I should have read the owner manual...not ever owning a 4WD truck before. If you have the key on...hold the 4WD HI button and the 4WD low button in at the same time for 3-4 seconds, it puts the transfer case in neutral and you can tow it with all 4 wheels on the ground with no damage to the trans. Wonders never cease.

I finally let my ASE certs go. More trouble than it was worth. They used to pay extra for having all 8 certs, like .50 cts per. Then they stopped doing ...SO. NO PAY....NO WASTING MY TIME. Over the years I trained a lot of kids out of UTI and such. Some are still working in the field and doing well. My last one kid I sold my "taco wagon" tool box to. Didn't need it, had one at home...so I just kept the tools. Now I have 2 or 3 of everything.

If you are going to Gillette in 2012 I bet we coulds swap some horror stories. BTW, when I was a snot nosed kid, I had a 34 5 window coupe (ferd) with a 331 ci" (punched to 340ci") Hem-ryoid with tri-power, Isky 808 cam, 10-1 pistons, port and polished heads with a 32 bolt hydromatic and a 9" ferd rearend. I built most of it myself. Wish I had it now. It was a REAL Henry, was full fendered and all the original lites, grill, bumpers and bright red. A 16 yr.old driving a cop magnet with a bulls eye painted on it. But man did it run hard...could pull the left front wheel about 6".

 

[Duramax1]

If your stuck in 5th at 55-60 take it out of T/H, let up on the throttle a bit and it will shift into 6th.

I agree.

But according to my Scanguage which provides me with a instantaneous gas consumption readout, the miles per gallon drops.
While the rpm's maybe lower, the engine requires more fuel to maintain the same speed.

For that reason I always leave my Allison in tow/haul mode when towing.

 

[porthole]

I agree.

But according to my Scanguage which provides me with a instantaneous gas consumption readout, the miles per gallon drops.
While the rpm's maybe lower, the engine requires more fuel to maintain the same speed.

For that reason I always leave my Allison in tow/haul mode when towing.

My point was that if the truck did not shift into 6th because the TH was active, turning it off will allow the shift. Once in 6th just turn it back on. I left out the last part.

TH only affects 6th gear by keeping the converter locked when you back off the throttle. That feature is for engine braking.

For engine braking to be effective the converter needs to be locked and the RPM's need to be high. That is why the Dmax Ally combo have such high RPM's when "auto downshifting"

Once I "slowed down" with the trailer I would use TH up to my cruise speed (55), turn it off, shift into 6th and then turn it back on. Sometimes a little extra speed may be needed, depending on the grade. But once in 6th I let the cruise bring it back on target.

 

[porthole]

Duane, the throttle blade (plate) should be just for air intake I would think. GM still uses throttle plates (blades) on most of its cars. Well at least our 07 Chevy Eqinox does.

(Bob, this will be mostly for the non automotive types here)
Just about all gasoline automotive engines use throttle blades for air intake.
Step on the throttle, the blade opens allowing air in. The blade angle is measured by a TPS (throttle position sensor).
This coupled with MAP (manifold absolute pressure) MAF (mass airflow sensor) and a host of other electronic wizardry and a PFM box or two is what fires off the injectors to run the engine.
Conventional 4 stroke gasoline engines use the piston intake stroke drawing a negative pressure (aka vacuum) in the manifold to start the process.

Diesels on the other hand don’t use throttle blades (same may have a blade but it is not for the same reasons as an automotive engine.
They still use many of the same controls though MAP’s MAF’s along “with a host of other electronic wizardry and a PFM box or two is what fires off the injectors to run the engine”.

If you were to crank over a gasoline engine with just a “snorkel” on top of the manifold and fire off the injectors, nothing will happen, because there is no control of the air fuel ration.

If you were to crank over a diesel with just a snorkel and fire off the injectors you have a running engine.
As long as the injectors fire the engine will run.
Want more speed – dump more fuel (injector pulse width and duration of pulse). Throttle position is used to control the electronics, not the air flow/vacuum that drives the gasoline engine.

Off the subject, I had the the 07 towed out of a snow bank. Another long story for later. The wheels kept locking up slightly when pulling it. HUMM, why did it do that...had it in neutral. So I asked our trans guy..."whats up with that"? Well I guess I should have read the owner manual...not ever owning a 4WD truck before. If you have the key on...hold the 4WD HI button and the 4WD low button in at the same time for 3-4 seconds, it puts the transfer case in neutral and you can tow it with all 4 wheels on the ground with no damage to the trans. Wonders never cease.

Before all the electronic gizmos you could do the same thing with the big transfer case stick on the floor. Now you have to read a book to find out you can do the same thing.

I “almost” had to have my 06 pulled out of the snow.
Went to my marina figuring it would not have been plowed yet. I was right – whoo hoo 2 feet of fresh snow to play in. When finished and heading for a “virgin” exit with a snow drift plow in front of it I slowed just down before exiting to let some people by.
That was it. Seems you can pack down a bit of snow under a truck. Just enough to lift the truck and take some weight off your tires.
45 minutes of shoveling for that.

I finally let my ASE certs go. More trouble than it was worth. They used to pay extra for having all 8 certs, like .50 cts per. Then they stopped doing ...SO. NO PAY....NO WASTING MY TIME. Over the years I trained a lot of kids out of UTI and such. Some are still working in the field and doing well. My last one kid I sold my "taco wagon" tool box to. Didn't need it, had one at home...so I just kept the tools. Now I have 2 or 3 of everything.

While still in the field and looking for a change I looked into teaching. Was offered a job at the county Vo-Tech. Great program. A good job, benefits, and they would send me to a special 2 year night school program (and pay for it) to get my New Jersey teaching degree.

I spent 3 days sitting in on classes. After that experience I said no way – I’d rather be a cop or fire fighter, it was safer.

If you are going to Gillette in 2012 I bet we could swap some horror stories.

It is on the agenda but no plans yet. Have to see how the year goes (and fuel)

BTW, when I was a snot nosed kid, I had a 34 5 window coupe (ferd) with a 331 ci" (punched to 340ci") Hem-ryoid with tri-power, Isky 808 cam, 10-1 pistons, port and polished heads with a 32 bolt hydromatic and a 9" ferd rearend. I built most of it myself. Wish I had it now. It was a REAL Henry, was full fendered and all the original lites, grill, bumpers and bright red. A 16 yr.old driving a cop magnet with a bulls eye painted on it. But man did it run hard...could pull the left front wheel about 6".

My favorite all time hot rod is the 32-34 3 window with the 5 window a close 2nd followed by the classic Willys

Your 331 should have been a “Fire-Power” Hemi.
Here is a bit of trivia – many of the 331’s that were used in hot rods came from the industrial side. The 331 Hemi was common in air raid sirens.
And – the first real “Hemi” was a V-16 monster that Chrysler built for the P-47 Thunderbolt. Proved the theory but that was during the war and production was job 1.