Duramax mileage blues

[franky]

I have a 2004 Duramax (diesel) with 10K miles. It is still only getting about 13 mpg hiway, 10 city. That is not what I was expecting. It is jacked 6" and has 18" wheels with 325R60-18 tires (not too tall)
I am told by numerous other owners (b.s. ers) even some with the same mods that I should be getting closer to 20 mpg which was what I was expecting.
Any body out there have the truth on MPG?

[Havasu Hangin']

Is that on the computer?

[Lightning]

Franky,
If you are going off of the built in shit, then you are way off - the speedo is off by a lot and your computer is off as well. You can always figure out the percentage difference in your tire diameter and then add it to the MPG that the computer tells you to get a closer to accurate gauge of gas mileage.
By the way, your motor is not even broken in yet. Your mileage will improve.

[franky]

Manual calculations are within 5% of what the comp stuff is telling me. i.e. if the comp says I used 24 gal, it holds about that.

[Havasu Hangin']

Originally posted by franky
Manual calculations are within 5% of what the comp stuff is telling me. i.e. if the comp says I used 24 gal, it holds about that.
The gallons are right...but the miles on the odometer are wrong.

[Mandelon]

My onboard computer says I get about 13 towing the boat at 75 mph......still unlifted and with stock wheels and tires though.

[77charger]

Originally posted by Mandelon
My onboard computer says I get about 13 towing the boat at 75 mph......still unlifted and with stock wheels and tires though.
I am getting 12 towing 80 with a gasser 6.0:D

[goneboatin]

Originally posted by 77charger
I am getting 12 towing 80 with a gasser 6.0:D
How the hell do you get 12 towing at 80 when I can't even get that not towing. I also have a Dogtec 6.0 :yuk:

[Jordy]

Originally posted by franky
Manual calculations are within 5% of what the comp stuff is telling me. i.e. if the comp says I used 24 gal, it holds about that.
Have you compared your speedo to say a GPS? You're going much further than the odometer thinks you are. I know on mine, with 285's I'm off by 5 mph at 55 and it gets worse from there. :D
Oh, and I'm getting 17 around town in my 2wd extra cab D-max company truck. It's bone stock on stock wheels and tires though.
I get around that according to the odometer highway in my '02 CC with 285's and all the goodies. :D

[hondajoey]

I am getting 11-12 MPG in a 8.1 Dually 4x4 towing,city, or highway as long as i keep it around 65.
but i love the monster

[boatnam2]

i have a 04 dodge with 37's at 60mph im of by 7 miles mph.

[TOBTEK]

Have an 04 duramax 4x4..thursday went from SD to orange county and back WITH a golfcart in the back with the top on (major air brake) aver's 17.8 thought that was pretty awesome:)

[OutCole'd]

Originally posted by TOBTEK
Have an 04 duramax 4x4..thursday went from SD to orange county and back WITH a golfcart in the back with the top on (major air brake) aver's 17.8 thought that was pretty awesome:)
That's incredible, is it down hill both ways???:D
I'm getting about 15 on average.

[Jrocket]

well i have a truck and i get 30mpg and the faster i go the better it gets and when i tow i get 70 mpg and when i go fast fast fast i get 100 mpg and then i slow down and then i speed up and one time i stopped and then i went fast ok.

[nodigg]

Ya know, I came down here to help me decide it I really wanted to trade my Avalanche for the diesel. I'm getting 16 mpg average overall. I would have expected more from the diesel. Of course it is a LOT heavier than mine.
There seems to be a wide variety of mpg figures coming from you guys. I wonder if it is driving styles or bad math?? Which rear end ratios do you have?

[TOBTEK]

Originally posted by nodigg
Ya know, I came down here to help me decide it I really wanted to trade my Avalanche for the diesel. I'm getting 16 mpg average overall. I would have expected more from the diesel. Of course it is a LOT heavier than mine.
There seems to be a wide variety of mpg figures coming from you guys. I wonder if it is driving styles or bad math?? Which rear end ratios do you have?
rear ends....and HOW YOUR DRIVING IT will make a HUGE difference. When im driving like a citizen, I get great MPG. When the JUICE is on level five as well as the low fuel boost, the ole MPG isnt so good;) ,,,but sure is fun blowing away all the rice rockets. has anyone else "black clouded" anyone:D ...man thats bad..hehehhe,shuckle,shuckle......

[nodigg]

Another question. How is towing with the Mitsubishi as far as soot getting on the towed vehicle? With or without a chip?
Not Mitsubishi! Izusu! OOPS!

[TOBTEK]

Originally posted by nodigg
Another question. How is towing with the Mitsubishi as far as soot getting on the towed vehicle? With or without a chip?
its not bad at all in stock form(little to no soot at all!)....but if you crank up the low speed fueling...bad, very bad! They dont requimend having the settings cranked up while towing anyway, to keep the heat down.

[nodigg]

That's good to know. The last diesel I had any first hand knowledge of, (Ford) was a TERRIBLE soot maker!

[Jrocket]

Originally posted by nodigg
Another question. How is towing with the Mitsubishi as far as soot getting on the towed vehicle? With or without a chip?
Mitsubishi?

[nodigg]

Originally posted by Jrocket
Mitsubishi?
Yeah, the Duramax is a Mitsubishi commercial diesel. I mean ISUZU!

[Magic34]

Originally posted by nodigg
Yeah, the Duramax is a Mitsubishi commercial diesel.
I thought is was an Isuzu?????

[Magic34]

I get about 8 MPG (based on Computer on dash) towing at 60-65 MPH. I cant seem to get better than 13.5 in town.
I like the power difference, but the MPG are a little disappointing compared to my 6L Chevy I had last year. Only about 1.5 MPG difference between the two towing.
Also, I am running 325/60 R20 tires, but they should make that much of a difference, should they?

[nodigg]

what rear end ratio do you have? do you have a chip? allison trans? are the tires you are running taller or shorter overall than stock?

[nodigg]

Originally posted by Magic34
I thought is was an Isuzu?????
MY BAD! I meant Isuzu! (BAD spelling?):confused: :rolleyes: :D

[CARGUY]

Originally posted by nodigg
Yeah, the Duramax is a Mitsubishi commercial diesel.
The Duramax is an Isuzu/GM partnership.

[RexRathburn]

A friend of mine just drove to Iowa with his 2002 Crew Cab Duramax (all stock) and got 16 mpg not towing anything. I thought it would be better than that? He said he's getting 13 around town.

[nodigg]

Originally posted by CARGUY
The Duramax is an Isuzu/GM partnership.
Yup, my bad! i'z just stoopid that way!

[nodigg]

Originally posted by RexRathburn
A friend of mine just drove to Iowa with his 2002 Crew Cab Duramax (all stock) and got 16 mpg not towing anything. I thought it would be better than that? He said he's getting 13 around town.
What rear end? 4wd or 2wd? 65mph or 85 mph?

[CARGUY]

Originally posted by nodigg
What rear end? 4wd or 2wd? 65mph or 85 mph?
Last time I checked Duramax is only avail in a 3.73 and I am sure this has not been changed for 05.

[nodigg]

Originally posted by CARGUY
Last time I checked Duramax is only avail in a 3.73 and I am sure this has not been changed for 05.
So no higher tow capacity, 4:10 is offered??

[CARGUY]

Originally posted by nodigg
So no higher tow capacity, 4:10 is offered??
I just double checked this for you and there is no change in the 05 order guide, the 3.73 is only rear end avail on 2500 and 3500 with the Duramax. 4.10 rear end is avail in 6.0 and 8.1 but not Duramax.
I remember this rear end ? coming up at a GM mtg and the Powertrain guys said the 3.73 is the best combo with the Duramax torque curve.

[nodigg]

Well, I can stop asking that question then. No 4:10 with Druamax.

[RexRathburn]

Originally posted by nodigg
What rear end? 4wd or 2wd? 65mph or 85 mph?
He said it's a 3.73 rear end, 4wd, and he was doing around 75.

[Magic34]

Originally posted by nodigg
what rear end ratio do you have? do you have a chip? allison trans? are the tires you are running taller or shorter overall than stock?
Allison trans is the only thing that comes with the Duramax.
My tires/wheels overall are taller than stock. I think it is almost 32.5-33 inches tall overall.
Chip and exhaust is being installed this next week, so I'll post changes once I have them done. I heard one of the air intakes out there will improve about 3 MPG. Is that even possible????

[nodigg]

disappointing but good info fellas...now, what to do about keeping the Avalanche...................16 combined mpg vs ???for 10k more? And I loose my car like ride......If only they could do air bag suspension and lighten them up a bit...........:confused:

[SoCalOffshore]

The ride in the 2500HD is awesome, sjust like my Z06. :D

[nodigg]

Originally posted by SoCalOffshore
The ride in the 2500HD is awesome, sjust like my Z06. :D
;) :D
How about the new Vette? DAMN!

[Back Forty]

I have a '98 Dodge with the 24v. It's a 4x4 dually 5spd ->stock everything. Speedo against gps reads about 1 mph fast above around 30 or so. Hand calculated I average around 17.5mpg. I was getting about 15.5 doing 80mph coming back from Missouri with the runabout in tow. I kind of expected more based on what I see some people claiming but overall the diesel kicks the ass of any gas vehicle I've had. I'm sold from here on out although I am hoping to hear better results about the newer offerings. I'll probably look to step into a new model on the next purchase. That may be a while based on what people keep reporting about the newest trucks from the big three.

[Kilrtoy]

After reading all this I found your problem
CHEVY
Seriously wow that is not good but I see the common theme, your speedo is way off.
So how do you fix this problem

[Dr. Eagle]

After reading all this I found your problem
CHEVY
So how do you fix this problem
You don't buy a Ford... that's for sure!!!!!!

[SHAKE-YO-AZZ]

should have got a ford