# Duramax MPG's



## EXR (Apr 1, 2009)

I just calculated the last two tanks in my truck and the one tank I got 9.4MPG and the other 9.6MPG. I did a calcualation few months back and it was around the same. This time I made sure to check after I had some fluids changed (oil, front and rear diff).

This is mostly city pulling a 16ft landscape trailer with total weight of 6000lb with equipment/trailer combo with multiple stops during the day.

I know Triple L is getting 450-500km per tank on his truck....I only get 350kms per tank. Just for the record this is exactly what I got on my 03 2500 ext cab short box 6L same set up. I have owed my dmax for over a year and havent hit 375kms per tank pulling my gear yet.

Oh and I run 265/16 AT tires (nitrogen filled).

Anyone else getting terrible MPG's on the 07 and up NBS dmax?


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## GMC Driver (Sep 9, 2005)

Can't say I've ever seen it that bad. Even pulling the 36' RV it does better than that.

Right out of the box it was 14-16 MPG. Once the DPF fell off, it went to 18-20 MPG. Best tank ever was a few weeks ago - 845kms on the 95 L tank.


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## mkwl (Jan 21, 2005)

Did you accomidate for the larger tire size in your calculations?

The DPF makes that much difference... glad my '06 doesn't have one!


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## badabing1512 (Aug 28, 2008)

You have a Edge Programmer on there? I know they were casuing some trucks to get ****** mileage, other than that do a full exhaust with a programmer that can erase dtcs and youll see a good 2-5 mpg improvement


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## Triple L (Nov 1, 2005)

He'd be stupid to put a tuner on it.... Or an exhaust... The trucks still under warranty, Thats the last thing you'd want to void expecially when its gettting this bad fuel economy cause you know somethings not right...

ps. Yesterday i took a little trip, total of 220 km's... Sure its all highway, but I was ripping on it the whole way, both ways, like 130km/h... And i burnt exactly 1/4 tank.... That woulda been like 3/4 tank for you


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## JD Dave (Mar 20, 2007)

Triple L;1064628 said:


> He'd be stupid to put a tuner on it.... Or an exhaust... The trucks still under warranty, Thats the last thing you'd want to void expecially when its gettting this bad fuel economy cause you know somethings not right...
> 
> ps. Yesterday i took a little trip, total of 220 km's... Sure its all highway, but I was ripping on it the whole way, both ways, like 130km/h... And i burnt exactly 1/4 tank.... That woulda been like 3/4 tank for you


You have to fill up your tank to see how much fuel you really used. The top 1/4 of your tank seems to last forever the bottom 3/4 goes very fast. Also I notice on our NBS trucks that the fuel light comes on way before it needs fuel . I'n the 9 years I've had my LB7 I have never got over 21 mpg. Our reg cab LMM has got 21 mpg at it's best on the way home from CT when it was brand new. Around town it's gets in the 14-17 mpg range depending on how you drive it. I would never do anything to a truck to void it's warranty.


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## EXR (Apr 1, 2009)

Triple L - 
had the truck looked at yesterday, e brake is not sticking and all four wheels rotate fine (no wheel bearing issues). I got them to rotate the tires while they had it in the air.

I was told to accurately get the right MPG's you fill the truck, drive to 1/2 tank write down the kms to 1/2 and the fuel required to fill back up. Do that 3 tanks to get an average using the data. On average I get 165kms to 1/2 tank using roughly 44L of diesel. 

I'm booking an appointment with the GM dealer to scan it and look it over for injector or fuel related issues (btw I changed the fuel filter last month). 

Oh and someone mentioned about the bigger tires (I run 265 on 16's). Triple L runs 20's with 305's (nice set up dude looks sweet) and gets 100km more per tank then me in a ext cab.


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## GMC Driver (Sep 9, 2005)

JD Dave;1064664 said:


> I would never do anything to a truck to void it's warranty.




I know you mean the farm truck...


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## Triple L (Nov 1, 2005)

JD Dave;1064664 said:


> You have to fill up your tank to see how much fuel you really used. The top 1/4 of your tank seems to last forever the bottom 3/4 goes very fast. Also I notice on our NBS trucks that the fuel light comes on way before it needs fuel . I'n the 9 years I've had my LB7 I have never got over 21 mpg. Our reg cab LMM has got 21 mpg at it's best on the way home from CT when it was brand new. Around town it's gets in the 14-17 mpg range depending on how you drive it. I would never do anything to a truck to void it's warranty.


I agree on the old body style trucks 100%, you could easily go 100 or more km's before the guage even moved... But i find my new one to be quite a bit more accurate...

Im gonna go fill it back up again today just for kicks, and figure out what mpg it gets cause I've never really done it and im kinda curious now....


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## JD Dave (Mar 20, 2007)

EXR;1064667 said:


> Triple L -
> had the truck looked at yesterday, e brake is not sticking and all four wheels rotate fine (no wheel bearing issues). I got them to rotate the tires while they had it in the air.
> 
> I was told to accurately get the right MPG's you fill the truck, drive to 1/2 tank write down the kms to 1/2 and the fuel required to fill back up. Do that 3 tanks to get an average using the data. On average I get 165kms to 1/2 tank using roughly 44L of diesel.
> ...


Your getting 8.9 US mpg and I get better then pulling 13,000 lbs avg more then 65 mph. It doesn't matter when you fill your truck up with fuel as long as you mark down the km and amount of fuel used/tank.


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## Triple L (Nov 1, 2005)

Just got back from the gas station....

Total milage - 230 km - 142 miles

Total fuel - 31 litres - 8.19 US Gallons

= 13.48 km/100 km or 17.45 mpg / US gallon

And thats ripping on it (even my dad was like, I think you should let the turbo cool down a little HAHAHA)... Plus my truck has a dump insert in it, catching a little bit of air, plus the 305 tires should add to the rolling resistance....

And that supports my origional average of 450-500 km/tank cause 230 got me to 3/4 tank... So even if the last 3/4 goes the quickest it still adds up...

There is defentially something wrong with your truck man...


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## Q101ATFD (Oct 24, 2006)

EXR;1063878 said:


> This is mostly city pulling a 16ft landscape trailer with total weight of 6000lb with equipment/trailer combo with multiple stops during the day.


I think that's where a majority of your perceived MPG problem is coming from. How many miles/kms are on the truck now? The Duramax engine doesn't really hit its MPG prime until around 30,000 miles or 50,000 km. City driving with short trips and multiple stops and a trailer won't produce favorable MPG on any engine. I don't really think 9 to 10 MPG is bad for the driving scenario you are describing. You have a really heavy truck, and a decent trailer that is in constant stop-and-go. If you really want to test your mileage, top off the tank and take the truck on a 100 mile trip on the highway at around 60 to 70 mph and see the results.


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## JD Dave (Mar 20, 2007)

Q101ATFD;1065007 said:


> I think that's where a majority of your perceived MPG problem is coming from. How many miles/kms are on the truck now? The Duramax engine doesn't really hit its MPG prime until around 30,000 miles or 50,000 km. City driving with short trips and multiple stops and a trailer won't produce favorable MPG on any engine. I don't really think 9 to 10 MPG is bad for the driving scenario you are describing. You have a really heavy truck, and a decent trailer that is in constant stop-and-go. If you really want to test your mileage, top off the tank and take the truck on a 100 mile trip on the highway at around 60 to 70 mph and see the results.


What he said. We need to compare apples to apples.


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## Triple L (Nov 1, 2005)

I figured myn out, average towing the idential same trailer as EXR, Same mowers and everything, except I carry a walkbehind and alot more trimmers and hand tools... and it comes out to about 13.2 - 14.5 mpg stictly city driving...

Maby it is driving style, but it still seems his economy is still kinda low...

On a side note, Since pretty much new, I've ran that lucus top end lube, just put a little in every tank, says its suppost to help mpg's... i dont really care about that tho, i add it to keep the cp3 lubed up a little more... my truck only has 25,000 km's on it so i guess its not even broken in... but its getting close to 1,000 hours so I think its more then broke in...

I forget, but exr's truck only had like 1,100 or something like that... So these are as close to apples to apples as you can get...


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## EXR (Apr 1, 2009)

/\ exactly. We have almost the identical pulling set up.

I'm taking it into the dealer.

I will post what they find.


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## bsmitty (Jun 27, 2010)

Hope this helps but I get 16-18 MPg around town on my 2004.5 LLY duramax. I put an Exhaust from the turbo back and a programmer on it. I am going to put a air induction system on it from banks to match the exhaust and programmer and hope to get a few more MPG's. Pulling my 4400lb. boat I get 18-19.6 MPG all day long. No problems in the MPG's here for me. I love the my truck!!


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## Triple L (Nov 1, 2005)

Well I got done my testing for the week...

My truck burns, on a bad week of more less ripping on it all week (went into regen. twice, usually it only does it once / week)

6.5L / hour...

Crazy cheap when you actually think of it, but I bet i can get that down to 5L / hour no problem on a more normal week

Also got 450 km to that last tank....


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## JDiepstra (Sep 15, 2008)

What is your gear ratio? Have you adjusted your speedometer to account for your larger than stock tire size? How hard do you drive this truck? What is the air pressure in your tires? Does it blow black smoke? Does your oil level ever go up? Do you have a lot of idle time?


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## Triple L (Nov 1, 2005)

3.73, i havent adjusted the speedo, but its off by vary little... 50lbs in all the tires, cant blow back smoke with the dpf, never check the oil, fair idle time, I dont turn it off everytime i get out... Im the one getting good fuel economy IMO... Just trying to help EXR out, maby he can test and see how many hours he gets on a tank of fuel...


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## JDiepstra (Sep 15, 2008)

Triple L;1074937 said:


> 3.73, i havent adjusted the speedo, but its off by vary little... 50lbs in all the tires, cant blow back smoke with the dpf, never check the oil, fair idle time, I dont turn it off everytime i get out... Im the one getting good fuel economy IMO... Just trying to help EXR out, maby he can test and see how many hours he gets on a tank of fuel...


Hey man, sorry, I guess I didn't clarify I was asking the OP for some info! But thanks for posting... you're getting some good mileage! I thought I read you were running 305's? If I do recall that correctly, it would have your speedo off by a good 10%.


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## Triple L (Nov 1, 2005)

ya i guess, i dont think its that much tho... But really, when im doing 55 im really going almost 60... so my fuel economy should be even higher and better cause im underdriving the odometer this way... haha, wow, now my truck gets really good fuel economy compared to exr's LOL


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## JDiepstra (Sep 15, 2008)

Yeah man you must drive like a grandma. HAHAHHA jk


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## EXR (Apr 1, 2009)

I delivered my Ferris to Kincardine on Saturday to a guy who bought it from me. I brought the walker along too just to see what MPG's I would get on the 4hour round trip.
To my shock, I got 16mpg...which is almost double what I get in the city.


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## Triple L (Nov 1, 2005)

thats not bad for towing both machines up there at all... Seems you just need to take it easier in the city....


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## the new boss 92 (Nov 29, 2008)

my dads 04 6 leaker got about 10 in the city, i dont think you doing to bad in the city, every were my dad goed his foots to the floor to. on the highway he got 14.5-16 i think your trucks fine. diesiels can dubble just be avoiding stopping and going.


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## EXR (Apr 1, 2009)

When I first got the truck summer 2009 I ran it up north on a 600-700km road trip and it got 18mpg unloaded with just me in it. I havent had a chance to try that again so thats why I brought both machines to see the hwy pulling mpg's.

Honestly I'm really not hard on the truck in the city..maybe its just the constant site to site to site to site travel everyday all day 5 days a week i dunno.


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## abbe (Sep 8, 2009)

My 7.3 gets better mileage driving from nh to ri with a 8'xblade on the front at80-85 then normal citydriving....howsthat for wierd


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