What Fuel Economy on GM 6.0L

[TBow]

In the spring, I sort of set my sights on a GM (Sierra or Silverado) 2500HD with a Duramax diesel. The main reason was so that I could realize some fuel economy on a full size pickup. But just about every Duramax from 05s to 07s that I looked at were running anywhere from $7K to $13K more than their gasoline little brothers. So I have reluctantly, and monetarily, eased my expectations down to a gasser.

My old Dodge Ram will only give me about 15 mpg on a good day, and I was hoping to realize something in the 18 to 21 mpg in a "new-to-me" truck. So I've been browsing just about every used car inventory website in Ontario to get a handle on what was available and what kind of price range I could expect. I'm still set on a Sierra or Silverado 2500HD extcab, 8', 4X4 from 05 to 07, and prices vary from about $16K to just under $25K. I'm not big on options and don't want leather and all the interior trimmings so an LS series in 06 or 07 (classic body style) should run around $19 to $20K I expect with the kms at or around 100K.

All of the gasoline 2500s I've looked at have the 6.0L.

1. What kind of fuel economy can I expect from the 6.0L? Is 20 mpg (hiway) realistic?

2. What differential ratio should I look for to best meet my expectations for better gas economy and still maintain some hauling power when needed? Is the rear differential ratio reflected in the VIN number?

The only hauling I do is a 7' x 14' tandem axle aluminum utility trailer and the largest load is really only for one week a year when I go moose hunting, so I don't think I need 4.10s. I am thinking of getting a 25' boat next year, so I'm pretty much set on a 2500. Plus I'm sick of having oncoming vehicles flashing their headlights at me on my trip north to moose hunt because the tongue weight on my trailer is pointing my front end (and headlights) skyward, even though I've had additional leafsprings put in my Dodge. I always try to balance my trailer load, but that combined with the load I carry in the box, just makes her squat to some degree.

TBow

[wtnhunt]

Look forward to seeing some replies here.

Likely gonna get a new to us truck this spring after we get our durango paid off. We need a 4 door, our 98 ext cab is just not working our for us anymore. Looking at an 08 or 09 gmc sierra or chevy silverado in the same config(2500 ext cab 4wd). Since it was around a $7500 option new I am kinda surprised that used that the diesels are bringing as much more as what they are over the gas models, but have noticed that where I have been checking as well.

[Shaun_300]

Well Tbow, usually you won't get any better than 14-15mpg with a 6.0L in that size of truck, Realistically it's around 12mpg. That's without towing. I believe they only come with 4:10s so you don't have much of a choice, unless you went to an 07 (new body style) and up, they have 3:73's with the new 6 speed transmission. They get a little better fuel economy. The 6.0L is a good engine, lots of snort to pull pretty much anything you want with it. The 8.1L is a BEAST when it comes to towing. It's a 496 fuel injected with a vortec style intake. I imagine 12-13mpg would be the norm for fuel economy for them.

[TBow]

12-MPG? OUCH!!!!!!!

Hoaky smokes Batman! From what I've heard and read about the Duramax diesels, 21 to 22 mpg was atainable, and possibly more if you opted for one of the aftermarket engine / fuel programmers. With that kind of savings with a Duramax and the low ratings for a 6.0L gasser, it sort of puts the Duramax back into consideration.

Everyone kept asking why the heck I was going for a Duramax when it was averaging $10K more per truck. They kept saying $10K would buy a lot of gasoline, which is right. But to double my fuel economy would save me about $200 per month at least if not more on fuel acquisitions alone. A loan for a $19K truck plus taxes for a gasser would run about $400 per month for 60 months and a 60 month loan for a $29K plus tax Duramax will run near $650 per month. It's starting to put the Duramax back into the running.

It was suggested for me to look stateside for a Duramax as prices were reportedly cheaper there. Even after the applicable exchange, taxes, fees at the border and cdn inspection and upgrade fees, I was told it was cheaper. Well I toured the US Autotrader sites and Ebay to get a perspective on price comparison and didn't really see any savings whatsoever. In fact after all was said and done, I think a US purchase would cost me a little bit more. For whatever reason, I did notice that Quebec retail prices, were on average, $2K to $4K less than in Ontario for a compatible Duramax.

I hadn't been looking at diesel Fords or Dodges, as the Duramax was getting better recommendations from any mechanics I was talking to, but I may have to take another look. The Fords and Dodges were running anywhere from $3K to $5K less than the Duramax for a similar diesel truck with compatible options.

TBow

[wtnhunt]

My current 3/4 ton truck does really good to get 12-13 and that is with a 350.

The 6.0L is a good engine, lots of snort to pull pretty much anything you want with it. The 8.1L is a BEAST when it comes to towing. It's a 496 fuel injected with a vortec style intake. I imagine 12-13mpg would be the norm for fuel economy for them.

Does the 6.0 not utilize an mds system in the newer trucks Shaun? Kinda figured 2008 and newer models would with trying to get efficiency up.

Diesel prices are running about .50 a gallon more than gas around here, how much difference is there in maintenace on diesel truck engine versus the gas? Just a few things to think about.

[TBow]

I've got a friend who has a 2010 GMC Sierra with a smaller V8 (4.8L ?)and it has the mds system. It's a regular cab with a short box 4X4, 1500. He told me he's lucky to get 18 mpg. That's not all that great in my books for an engine designed to produce better fuel economy.

Another excoleague dropped by my house this morning to pick some materials up. He has a 2004, GMC 2500HD with a Duramax. It's a crew cab with short box and he uses it for hauling his 5th-wheel trailer. He told me he's getting 24 mpg hiway without the trailer, and 17 mpg trailering. That's pretty good in my books. He's 65 years old, so I'm sure his driving habits play nicely into getting better fuel economies as he's apt to keep things at or around the speed limit, unlike most who see a 50 MPH / 80 KPH speed sign and immediately interpret it as 60 MPH / 100 KPH.

He did say though that a sensor went on the engine, and cost him $1100. His fuel injectors are still original, but I have it on good authority that GM extended the warranty to 230,000 km on the injectors. If you had to pay out of pocket for injectors on a Duramax, it's gon'na run you $3000 to $4000 I was told. I had a 2003 Duramax at my old job and we used it for hauling 23 to 25 foot boats almost exclusively. The guys I worked with told me it's got over 300,000 km on it right now and has had the injectors replaced twice, all on GM's tab.

Diesel fuel is currently cheaper than gasoline prices around where I live, but that can change anytime. A couple years ago diesel cost more than gas. Gas is running around $0.999/L and diesel is about $0.939/L right now.

So I've definately ruled out a gas burning GM product at those kind of poor mpg results. Heck I might just as well run my poor old Dodge into the ground if I can't realize any savings on a "new-to-me" truck. So I'm back to researching Duramax prices and will keep my eyes on Kijiji, Autotrader and the local dealerships and private sales, but am not willing topay an arm and a leg for a 4 to 5 year old buggy.

TBow

[Shaun_300]

It really all comes down to the driver, I know the 6.0 in the newer style trucks are better on fuel because they have the 6 speed transmission which allows them to go to 3:73 gears. That with the closer gear ratios in the 6 speed trans allow for less revving to give the slightly better fuel economy. The older ones with the 4L80 had to have the 4:10 gear ratio to help the transmission out. Not all the time though do you need a higher gear ratio to get better fuel economy. It takes a lot less effort for an engine to hold 60mph with 4:10s than with say 3:73 or 3:42s.

My step-grandfather is from Ohio, he drives a 2001 Sierra 2500HD with the 6.0L. He says driving from here to Ohio on cruise he gets 14mpg. That's driving 70-75mph.

[wtnhunt]

It really all comes down to the driver, I know the 6.0 in the newer style trucks are better on fuel because they have the 6 speed transmission which allows them to go to 3:73 gears. That with the closer gear ratios in the 6 speed trans allow for less revving to give the slightly better fuel economy. The older ones with the 4L80 had to have the 4:10 gear ratio to help the transmission out. Not all the time though do you need a higher gear ratio to get better fuel economy. It takes a lot less effort for an engine to hold 60mph with 4:10s than with say 3:73 or 3:42s.

When was the first year GM coupled the 6.0 with the 6 speed tranny Shaun? Seems the trucks I have looked at online have all had the 6 speed, only been looking at 2008 and newer though.

[Shaun_300]

In 2007 William. There's 07 Classic style and 07 New style. The new style trucks from 07-present have the 6-speed in the 6.0L 3/4 tons. The only 6.0L new style truck with the 4 speed was the 1/2 ton Vortec Max trucks. In 2009 they started phasing the 6 speeds into the 1/2 tons too if they have the 5.3L in them. If they have the 4.8L or 4.3L V6 they still have the 4-speeds in them. The 6 speed takes a bit of getting used to, shifts a lot more with the 2 extra gears. Good tranny and nice one to work on too, they are based on the Allison. Only had a few 07 and early model 08 that had a minor issue, even though the tranny had to be pulled out to repair. GM addressed the issue with updated seals and haven't had another one apart since.

[Onlychevy6]

As with any truck. You can get a programmer to alter your fuel mpg among anything else you need. You can also get the computer reprogrammed to your driving style at a fair price.

[pendog]

I havent posted pics yet but i was just blessed to get my first new vehicle. i got a 2010 4 door short box sierra with a 5.3. it has the 6 speed, fuel management system. with only a thousand miles on it i am getting 16.5-17.0 with mixed city highway driving, we got 20.7 on the highway the last tank of gas.

[snapper]

My old '02 Silverado 2500HD crew got about 12 mpg with the 4:10 gears. My new '09 Sierra 2500 crew gets around 14 mpg with the 3:73 gears.

I had an '09 duramax with the allison for a weekend...put over 150 miles on it and averaged 15 mpg. Something to do with the "new" emmisions in the exhast is why the mpg sucked. After seeing the duramax as a $7,000 upgrade and the allison tranny over $2,000 and diesel costing around $.60 per gallon more than gas...I opted for the 6.0 again. Couldn't find a new truck with the 8.1 in it...wasn't sure if they even still offered that engine. Also, figure oil changes will at least double in cost with the diesel. Guess it depends on what you need it for...I wanted it...but not at that price and little mpg gain.

[TBow]

It's strange that I keep hearing mpg ratings for the Duramax diesels that are all over the board. One of my best friends drove a 3500 GMC Duramax for work. When new, it gave them 27 mpg hiway, no trailering. His boss that I just talked to last week has a 2004 GMC Sierra 2500 crewcab, short box Duramax. He told me he was getting 24 mpg hiway (not trailering) and 17 mpg hiway with a 5th wheel on behind. Another friend with a '03 2500 Duramax was getting 13 mpg hiway towing a 5th wheel 28' Toy Hauler.

I've talked to a few other Duramax owners, as I tend to just walk up them at the coffee shop if I see them driving in with one, and ask them how they like it and what their mileage is. I've heard everything from 18 mpg to 22 mpg in those instances. Driving styles has a lot to do with it too I guess.

One thing that is consistant from all that I've talked to, they haul like crazy!

TBow

[jcot2773]

Don't pull the fuel filter without a scan tool... i made that mistake never again with a duramax. you have to have the scan tool to prime from there. A friend of mine had a cummins that was getting 21 when he first bought it then one day it dropped to 15. and stayed there we changed out filters, everything we could and no change. about 2 months later his lift pump died and took the rail pump and injectors with it. we put a FASS fuel system lift pump 200hp bullydog rail pump 150hp injectors on it and an edge juice with attitude. all of a sudden now he gets 28 on the highway and 22 in the city. from the factory diesels are not set up very efficient at all.

[Shaun_300]

You do not need a scan tool to prime a Duramax. There's a bleeder screw on top of the fuel filter housing you crack open, push the primer until fuel comes out, close the bleeder, pump the primer another 20-25 times and away you go.

The newer Duramax trucks are harder on fuel than the older ones. In 07 (new style trucks) they went to the LMM Duramax which had quite a bit more power than the older ones, fuel economy dropped quite a bit. We had a lot of customers complaining that it was worse than their older trucks. They need to burn more fuel to make the power, so of course their gonna be a bit harder on fuel. I drove a new 2011 Duramax the other day, which is the newest one with the DEF fluid you need to add, exhaust brake, etc. It has 397hp and 765lb ft of torque. Holy CRAP does that thing ever get up and go! I bed it'd take a Silverado 6.2L :jaw: It'll be interesting to see what these ones are like on fuel. Guess it will be worse no matter what way you look at it, when you need to fill your DEF tank every 10,000 miles or so with $300 worth of fluid.

[TBow]

Shaun, you wrote:

The newer Duramax trucks are harder on fuel than the older ones. In 07 (new style trucks) they went to the LMM Duramax which had quite a bit more power than the older ones, fuel economy dropped quite a bit.

I have my eye on an 07 Silverado 2500 with a Duramax, but it's the old body style. I think they refer to that body style as "classic". I'm not really a big fan of the GMC / Chev newer body style.

Did the classic body style in 07 have the same engine that you made reference to for the newer 07 body style in the quote?

If so, then I'll be backing my expectations up to an '06 or '05, because this acquisition is based primarily on better fuel economy for me. I would readily jump at better fuel savings over greater power due to my hauling requirements being modest at best.

TBow

[Texan_Til_I_Die]

As far as I know, the 07 Classic body style always came with the LBZ engine. That's the one all the diesel guys like. My 07 is the new body style and has the LMM engine. I have the Crew Cab 4x4 and somewhat oversized tires on it and I can squeeze out 21 MPG highway if I take it easy. 17 MPG is a more normal figure for highway/city/ranch driving combined. Plus I'm bad about not killing the engine for short stops. And my mileage went down a little bit last year with the EPA mandated diesel formula change.

[Shaun_300]

Yep the LMM was introduced in the 07 new body style - 2010 trucks. LBZ are in the 07 Classics.

[LETMGROW]

I honestly think gas mileage is one of the most lied about topics in the universe. Perhaps only behind deer hunting and fishing.

NOBODY wants to admit they get less mileage on a vehicle than their buddy gets.

In reality, Shaun was on the money with his 12 to 14 or 15 for the 6.0 3/4 T. trucks. That is on a good day. Expect much more and you are going to be disappointed.

My 5.3 is a little better but it doesn't make gas!

All my offroad equipment is diesel and I wouldn't have anything else. I don't have a use for a diesel truck personally, but I would probably own one if I did.

In my neck of the woods diesel road fuel runs about 30 cents more per gallon than gasoline.

Lynn

[TBow]

In Ontario, diesel fuel is less than gasoline by about $0.04 or $0.05/litre which works out to about $0.20 less per gallon.

I've talked to a lot of Duramax owners to get their real world ratings on fuel economy and I also had a Duramax in my shop before I retired. Realistically, fuel ratings of 21 or 22 mpg for the big 6.6 is attainable by all reports I've received with some as much as 27 mpg (and everywhere inbetween). If I could realize 22 to 24 mpg hiway, I would almost double my gas mileage from my Dodge Ram with a 318 that I'm driving now.

BTW: Bear in mind that an Imperial gallon (in Canada) is 1/5th larger than a US gallon, which may attest to greater gas ratings here in Canuckistan.

TBow