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Discussion Starter · #1 ·
Ok, I'm about sick of it. I've had two of these trucks and both have been gulttons of Diesel fuel. The first truck got about 12 or 13 mpg, all stock. I now have had my 03' for more than a year (first time in 4 years to own a truck more than 365 days) and it's only getting about 11 to 12 MPG. I really enjoy the truck but this damm MPG thing is the pitts! The truck does not have a fuel leak, water leak, oil leak or a bad transmission. However, it does have some "go-fast" stuff in it. I've tried everything in the book to get better MPG and it just won't do. Last year I drove the truck 800 miles "stock" to my hunting lodge with a trailer and got 14 MPG staying close (+/- 3mph) to the speed limmit. This year I do the same thing but... I've got H2 wheels with 33" mudders, Uni air filter, full Banks exhaust, Pred, more springs, The "HOT" Juice/Attitude (fuel on 3 Level 1) and twice the trailer I had last time. My AVG speed was.... well, put it this way. I drove 306 miles in 4&3/4 hours with two stops. This trip yeilded 11.5 MPG. Is it just me or have I gotten two lemons back2back?


--- the 03' gets Delvac 1 oil, mobile 1 grease, new filters every 5k on "everything" and Stanadyne for the last 4k miles.





I have just about had enough. If this MPG thing is not resolved, I'm done with GM Diesels and maybe GM as a whole.





Burner--------->
 

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Discussion Starter · #3 ·
I took off my 305 Nitto's to run the 33 Mudders during hunting season. Yes, my speedo is correct, see pred in description. Even my attitude is correct. All calibrations were performed with Garmin GPS's, I use two.


I wonder if the fuel PSI could be the problem or a "bunch' of injectors? I am leaning tward the pump being that the rates are around -1.9 to +3.


.......... if only Eric had my truck for a week........


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No I Was Just Thinking Even 305's You Will Still Lose mpg With Bigger Tire, And Wrong Speedo Makes It Worse. I Lost mpg Going From 245 to 265 With Speedo Corrected


JUST THINKING:As Far As Rates Those Are Ok
 

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Let me see if I am understanding your statements correctly.
You drove 306miles/4.75hours (~65mph) pulling a trailer that is twice the size as before with 33" tires on winter fuel. If so, 11.5 mph doesnt sound to bad. Im sure if you had a 502 gasser you would be near 6 to 8 mph.
 

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I don't know what you're bitching about. That IS good mileage under those conditions!


I towed about 9K worth of tractor and trailer 900 miles in about 14 hours, got about 11 MPG and was thrilled. That is all stock except a Quad on the 50 HP tune.


You're running 33s and towing at 70+ MPH, just what do you expect!? I'd say you're right in the ballpark and probably doing better than should be expected. If you think you can do much better with another make, go for it, but I think you will again be disappointed.
 

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Are you getting 12-13 mpg empty or towing? It wasn't clear in your post. I have a 4" lift and running 35's and consistently get 16.X (emtpy) and that is corrected MPG by multiplying mileage by 1.28 for the 35's.


I'm assuming your correcting for tire size when figuring the mpg? Not sure what I get when towing a 25' toy hauler but my thought has always been it doesn't matter ... as I drive the truck empty 95% of the time.Edited by: tophog
 

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Burner,


I pull a 30' fifth wheel that goes close to 9,000lbs. and a front like a barn door. My tires are stock and I pull with the Juice on level 2. I average 10-12 depending on terrain. I run 75 most of the time. I am damn happy with my MPG. My 1998 454 could hardly better that empty!!! Running without the trailer and Juice on level 4 I get 18.5MPG at 85 mph. Best I have ever gotten was 19.5 for a tank. Running back and forth to work half freeway it's usually 16.5 my 1998 gasser got 10.5.
 

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Discussion Starter · #10 ·
The 02' truck's AVG "over all" MPG was around 12 and the "over-all" MPG on the 03' is around 11 mpg. There are some tanks that just "sit and burn" and I do toss those out. It does seem as if the truck burns as much at idle as it does @ 60mph in 5th?


I have "never" attained one tank or even a 1/2 tank of fuel that returned 16MPG in either truck. Heck, my 2000 6.0 returned 17 MPG on a 400 mile trip to the mountains. My 01 Yukon XL with a frick'n 8.1 liter gave me 14.1 (empty) MPG and 12.8 (U-Haul TDM axel) on the return home and that was 800 miles each way. I don't know what to do.... I hated that dang Ol'e Dodge but the Cummins just purred along sipping fuel to the tune of 19 MPG.


I want my cake and eat it to, I just don't want to be beheaded for it. ....... Buy a GMC and get all the goddies and a strange but good motor that's a lush on Diesel. Buy a Dodge and feel like you're in a really nice 1970's truck. I guess Ford is the only other thing out there? I wonder if they ever got those funny "darting" brakes fixed. My 01' PS almost wrecked me on a washboard gravel road and then about killed me on the Hwy with the wicked brake pull...sometimes right and sometimes left.


Burner--------
 

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Discussion Starter · #11 ·
2000 Chevy 6.0 4x4 Ext Cab Avg MPG = 13 24k


2001 Yukon XL 8.1 4x4 Avg MPG = 10.4 44k (still have it)


2001 PS 7.3 4x4 Crew Cab Avg MPG = 11 27k


1999 Suburban 454 4x4 Big tires Avg MPG = 10 33k


2002 GMC 6.6 4x4 Crew Cab Avg MPG = 12.5 24k


2003 GMC 6.6 4x4 Crew Cab Avg Mpg = 11 32k


In all fariness, the 98' Dodge spent lots of time on the road which ment it was not fair to compare. Also, the PS spent many many hours at Idle.





What gets me is the MPG on the Gas vs. the Diesel. ..........





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I dont see what there is to complain about. You drive fast, have several power mods, big tires and are pulling a trailer and still got decent mileage. If you want better mileage ... put back on the stock tires, take off all power mods and pull at a fuel friendly speed.
 

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Put the stock exaust back on while you are at it. I lost a 1 MPH with my banks. Think it has somthin to do with my foot being connected to my ear.
 

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Discussion Starter · #14 ·
Hummm....... perhaps I have not stated things correctly.


Running a "stock" truck with "stock" tires pulling 2,000 lbs total trailer weight @ the speed limmit yeilded a week 14 MPG. Actually it was around 13.8 or so, I do not think that is good. My 6.0 would do that, my PS would do that or more and my Dodge/Cummins would maybe go down to 18 MPG...maybe. That's what bothered me........


On the "mod" run it should have been a little better than 11.5. The trailer weight was around 2500 lbs, a Rincon and Rubicon on a light 16ft trailer. It's not apples to apples but I think it's pretty reflective.


What do you think?


Burner
 

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Burner:


Well, my truck will do a little better than yours unloaded. I get about 18 (+ or - a little) at 70 - 75 MPH empty and you say you've never seen that, even stock. I was stuck around 16 MPG until some break-in occurred.


I see some guys getting better, a lot the same, and some a little worse (like you).


All:


It might be an interesting experiment for someone to chart the mileage reported in relation to truck configuration, i.e. CC vs RC, D/A vs D/ZF, etc. in addition to empty vs loaded, speeds driven, miles on vehicle, wheel/tire combos, power adders, etc., etc.. That is a lot of variables and I'm not sure any correlation could be inferred, but it might be fun to do. I suppose some things would have to binned to keep the variables under control and have meaningful sample sizes. I don't have time to attempt it just now.
 

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I used to have a 2001 2500 4x4 with the 6.0 and 4:10 gears. It would average 12-13 with a mixture of city-highway driving. If I towed anything at all with it the mileage really dropped. With my current rig the only pulling I have done with it was last fall on a hunting trip from Indiana to Colorado .... I pulled a single axle trailer that weighed 1300lbs empty with two 600lb 4wheelers on it as well as about 1000lbs additional weight. I also had about 1000lbs in the bed and an unusually high camper shell. This was before I had any mods to the truck at all ..... I got around 15 or 16mpg if I kept it under 65 but the mileage dropped to about 13 or 14 if I ran much faster than that. I seem to get about 18 or so empty with mostly town driving but this colder weather has seemed to drop me to 16-17 as an average.
 

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The variations in mileage that the DMax sees has been a continuing source of conversation. I've been very happy with my results. One thing that I learned in my previous diesel, a '99 6.5TD Tahoe, is that there are "sweet spots" in the diesel rpm range that really give great mileage and being as little as a couple hundred rpm to either side will show significant economy dropoffs. I don't miss much in comparison to the DMax, but one thing that I do miss is the electronically-controlled wastegate on the Tahoe. I could drive on the boost gauge on the highway and really increase my economy. If the system was boosting, it was burning fuel and running less efficiently. I could "tune" my rpms and speed to hit a spot where the computer was dumping boost because the engine was running "sweet." I got over 17 mpg running a 5x8 loaded U-Haul trailer across the Illinois/Indiana turnpike once this way!
 

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Discussion Starter · #19 ·
A little more info about the truck.


I'm really picky about the alliment. I've had the truck on the rack about 12 times or so. However, I've have had 4 sets of tires and three different rim combo's. I did have the truck allined before the trip "just-n-case" It was out. I think that the truck is broken-in..... It's got 32k with 1,430 hours on it.


---on the first trip, the "stock" run, it had only 3,000 miles on it.


--- My 2000 6.0 was a 4x4 Ext Cab SB with a 3:73 rear. Plus, it had the STEEL heads.


--- My 01 8.1 Burb does have the 4:10 rear


Burner
 
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