2006 3500 Mega/G56, Will I break 21 MPG?

[JBonpua]

After following this board for a while before I ever bought my truck, I’ve read the horrible fuel mileage on 3rd G56 equipped trucks getting less than 16 MPG. I was shocked when I checked mine (all hand calculated). When I first took delivery of the truck it got about 17. 5 at about @ 300 miles on the clock. At 1. 5k miles it got 18. 03. At about 2k miles I installed a Banks Monster muffler and got 19. 27. At a little over 5k miles I installed an S&B filter kit and was getting 19. 61Oo. . All driving is 90% highway 20% city. No mod on the truck that can possibly affect MPG except for the Banks muffler, S&B filter and Leer cap. From what I’ve read on this board and from the little piece of card that was hanging on the cigarette lighter when I picked up my truck, MPG will improve once the truck reach 10k miles…can’t wait.



I also try to do what I can to increase my MPG by coasting to stop signs/red lights and launching gently from 2nd and keeping my RPM under 2k on the highway. I know at 2k RPM I am only going about 63 MPH but I’m not always in a hurry so no big deal. If I need to be somewhere at a certain time, I just start my trip 5-10 minutes earlier.



My hope is to break 21 MPG when I reach 10k miles when I replace the engine, transmission & differential with Amsoil. I am also thinking about putting those Airtabs on top and sides of my cap. What do you all think?

 

[SBeretz]

I have the same truck as you and regularly pull 20 MPG hand calculated outta my truck. Mainly around home, at 55-60MPH. I have 25K miles on my truck and it keeps getting better. The only engine mod I have done is the muffler delete and switched to Rotella 5w40 which isn't even a full synthetic. Seems like trucks doing alright by me. Scotty

 

[9 Lives]

My 06 has 15K on the clock and has never empty gotten better than 14mpg towing around 9mpg. That's @ 75-80 on the highway.

 

[CSkal]

I have gotten 20+ since new. Of course, I drive like a granny...

 

[kbond]

what's promising about this is the auto guy's overdrive is taller so in theory we would be able to do the same.

 

[kowaliga]

Ditto CSkal, but in an '05 4x4 QC longbed/G56. I'm so slow Granny passes waving a finger, but I get great mpg.

 

[2broke2smoke]

we hand calculated for the first 12k on the wifes non mega '06 and the overall avg was 17. 8



last long trip to pa and back was 17. 8 up and 17. 7 back ...



filled up when i pulled onto the interstate and when i pulled back off both ...



set the cruise at 70 ...



i think the biggest variable with these motors is your right foot ...

 

[gsbrockman]

All driving is 90% highway 20% city.

That equals 110% ! :-laf

 

[Huskerman]

I used to obssess about mileage but I finally got over it when I realized that if I can afford the truck, I can afford the fuel.



Mileage is a pretty subjective thing and I have found that comparing mileage is dubious at best because it's rare that you find two people who drive the same route the same way.



HOWEVER!! If there is one thing that people have in common, it's this:

My 06 has 15K on the clock and has never empty gotten better than 14mpg towing around 9mpg. That's @ 75-80 on the highway.

Most folks I have seen that get really crappy mileage will tell you that they drive 75, 80, 85 and even 90 mph because if they don't they will "get run over". (yeah, RIGHT. I see crew cab trucks getting run off the road ALLLL time )



The sweet spots on these trucks (both 2nd and 3rd gen) is about 1900-2000 rpm. That is where you are going to get your best highway mileage. Unfortunately for some, that is somewhere in the neighborhood of 55-65 mph.



Huskerman

 

[CDonaldson]

It isn't so much about getting 'run over' as it is all the tailgaiting and the close pull-out's and pull-in's as they go around you. They all but 'swipe' your fenders off cutting back in sometimes. They cannot judge their speed and small vehicle size and start to cut back in way before they have a reasonable clearance to do so. That DOES get a little nerve-wracking and it sometimes is easier to just go with the flow of the traffic, so as a result we suffer on our fuel consumption.



I went to 315 tires to get the rpm's down into the sweet spot at 65+ mph speeds. Here in NM out highway speeds are 75mph and it is crazy to drive at the lower speeds to stay in the sweet spot. I expected to see a decrease in mpg's because all I have read here and on other sites. Much to my suprise my mpg's got slightly better. So the difference of rolling on stock tires at 65mph approx 2400rpm's vrs the taller tires at 65mph at 2Krpms actually was a gain in mpg's. When I go the speed limit of 75mph I am getting an average of 17. 5mpg empty, and 14. 8mpg towing >12K. I am running the TOYO AT's when getting that mileage. I have a set of 35" BFG AT KO's for winter tires and I loose 2mpg off those numbers, but also on winter fuel so I'm not certain of it is the tires or the fuel causing the difference.



CD

 

[jelag]

Years ago I spent a lot of time working with a chassis dyno... . After teaching tech's how to use them I must have at least 1000 hours working on them..... I learned several things... .

1 - we used to get a lot of guys selling stuff to improve the mileage, we offered them a chance to test and prove their product on the indoor highway... no one ever took us up on it... . but offered samples and none ever showed any improvement in fuel economy... . except Slick 50 in the engine, transmission and rear end... but at the time the cost of product and how often it had to be changed in the engine made it worth the investment...

2 - as speed doubles the wind resistance and rolling resistance quadruples... so from 20 mph to 40 mph the resistance goes up 4x's ect... . we used to take a vehicle out on the highway and get some standards for straight and level driving, and hill climbing and would re-create that on the dyno and test and test... .

3 - I've learned that when I want to get good mileage let my wife drive... she starts slower, drives at a slower speed, and never uses the brake because she for casts the traffic and stopping... . she easily gets 15-20% better economy than I do in any of our vehicles... . I just don't care.....

4 - when I had a chance to get next to an engineer I listened... their education base was awsome and often held bits of information that made me think... . Remember that if DC could get 10% better fuel economy with our trucks for say $1,000 invested they'd do it... Their under federal EPA mandates to improve C. A. F. E. , Corp. average fuel economy... which is an average of their vehicle sales annually... so often they are giving away a small car to offset the low fuel economy of our trucks... . There is no silver lining to this... with lower emissions there just is no good answer...

so the real key to better fuel economy is better wind tunnel development, which means all trucks will look the same... . smoother shifts and torque converters locked up tight so there is no slippage and loss... and limits on acceleration and top speed would make a huge difference... . remember there is a formula for the frontal mass, weight, and wind resistance for fuel economy.....

Well this is much longer than I thought it would be... ... I'm done... .

 

[Huskerman]

It isn't so much about getting 'run over' as it is all the tailgaiting and the close pull-out's and pull-in's as they go around you. They all but 'swipe' your fenders off cutting back in sometimes. They cannot judge their speed and small vehicle size and start to cut back in way before they have a reasonable clearance to do so. That DOES get a little nerve-wracking and it sometimes is easier to just go with the flow of the traffic, so as a result we suffer on our fuel consumption.



I went to 315 tires to get the rpm's down into the sweet spot at 65+ mph speeds. Here in NM out highway speeds are 75mph and it is crazy to drive at the lower speeds to stay in the sweet spot. I expected to see a decrease in mpg's because all I have read here and on other sites. Much to my suprise my mpg's got slightly better. So the difference of rolling on stock tires at 65mph approx 2400rpm's vrs the taller tires at 65mph at 2Krpms actually was a gain in mpg's. When I go the speed limit of 75mph I am getting an average of 17. 5mpg empty, and 14. 8mpg towing >12K. I am running the TOYO AT's when getting that mileage. I have a set of 35" BFG AT KO's for winter tires and I loose 2mpg off those numbers, but also on winter fuel so I'm not certain of it is the tires or the fuel causing the difference.



CD

Really good points. Me personally, if the speed limit is 75, I am not going to drive 65 just to get better mileage. My point was simply that when you go past 65, you can expect worse mileage.



About your tires, I thought that 315's were the same as 35's or at leaste VERY close. I don't change tires in the winter but I do notice a 2 mpg drop when on winter fuel.



jelag,



VERY informative!!! Thanks.



Huskerman

 

[CDonaldson]

Hey Huskerman.



Glad you brought up the 35 - 315 stuff. I actually have the 315-70-17 BFG AT KO's not the 35"ers. The difference in the two is about tire/track width. The 315-70-17's are right at 10" of tire width, the 35" BFG AT KO's are 12. 5" of tire width. They are both the same height of 35" - actually 34. 5".



I do not stay at 65 to get better mileage either. When traffic is rolling at 75 I go 75, otherwise you are almost a road hazzard with everyone cutting in/out, etc. I got your point, and it does change your mileage, NO doubt about that every time I fuel up.



I only change tires in the winter because of where I live. I live in a mountaneous area at 7K ft altitude. I run around from there up to altitudes of 11K ft, and everything in between. We sometimes get snow when it is not even called for - the weather service has great difficulty predicting our area. I have a set of the TOYO's on my older Ford ranch truck and they are horrible in the snow or stopping when a little ice is built up under the snow, even on dirt/gravel roads. The virtually have no grip, no side lugs, nothing. They are outstanding for wear on hot desert roads, but cold roads and bad road conditions they are like driving on slicks. If I did not have that problem I would not change to a winter treaded tire. I have run the BFG AT's year round and they DO hold up well to the hot roads but get sticky and decrease mileage in both tire wear and fuel. Once our temps get to 80 or so during the day I switch out for the TOYO's and more or less a summer/highway tread.



I saw the guy at the gas station today dumping in some new diesel, we are now on summer fuel as of today. That makes me real happy, better mileage on the horizon. Also, fuel costs rose $. 30/gal, we are at $2. 80/gal.



CD

 

[Huskerman]

315-70-17 BFG AT KO's

That's the same tire I am running. Almost wish they would wear faster so I could get the Toyo Open Country M/T. :-laf



Huskerman

 

[DJennings]

The difference in the two is about tire/track width. The 315-70-17's are right at 10" of tire width, the 35" BFG AT KO's are 12. 5" of tire width. They are both the same height of 35" - actually 34. 5".

315mm = 12. 4". A 315/75R17 is the same tire as a 35x12. 5/17 tire.

 

[Bob V]

jelag, good stuff. Vehicle weight and drag are big on fuel economy. A ladder rack can cost you 1-2 MPG and so can an extra 500 pounds. I thing I have found is if you keep under 600 deg, pre turbo will get the best mileage, this is from Clessie Cummins himself, I gained almost 3mpg just by doing that. Hard to do, especially up hill. I run 315 tires (35") and I lost about 1mpg, but have gotten up to 20mpg (HWY, 65-70) with my current set up.

 

[Mrudolph]

When I drive to Seneca SC from my home on 2 lane highways @ the posted speed of 55 = 24. 1 MPG hand calculated, the faster I drive from there the lower my mileage. Do I drive 55 on I-75 in a posted 70 zone, NO I drive the posed speed and at 70 my mileage drops conciderably down to 17. 5 - 18.