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What kind of MPGs can i expect with the 6.6L

93K views 39 replies 18 participants last post by  kingcheez 
#1 ·
I will be upgrading my 1/2 ton to a 3/4 ton soon with the 6.6 and was wondering what kind of MPGS you guys are seeing in the city? I have the 6.2 right now with 33's and getting around 11 or 12 in town and also on the highway doing 70 to 80. When i pull my 9000 trailer i got 7mpg doing 70 for an 8hr trip. I plan on using the stock wheels and tires on the 6.6 and hoping for at least 18 to 20 down the interstate at 70 and at least 14 in town.
 
#2 ·
I had an 07 DMax 4x4 ext. cab LWB (stock/no mods) as a work truck for a year. On highway, with no load, I'd get around 21 MPG's.
Also had an 08 DMax 4x4 Crew cab (stock/no mods) and it would get about 18 MPG's, but my dad's 08 DMax Crew is exactly the same except LWB and he gets about 20-21 MPG's with no load.
I've decided that I probably could have gotten better mileage on both trucks if I'd kept my foot off the floor a little more often. Awesome trucks though...
 
#5 ·
Just about any handheld tuner can add triple-digit HP gains... kinda crazy, but they work.

I've also heard that diesels get better MPG when towing vs. gas engines. I can't say I've personally seen that, since I don't have a Duramax :(... maybe in a few years.
 
#6 ·
Don't drive in the city much, but about 14-15 from what I've seen. After 8000mi I'm averaging 19mpg mixed suburban and freeway commuting. Mountain highway either empty or level filled bed I started out about 20mpg new, and my last 500 mile trip averaged 22.5 mpg. With 11,000lb 5th wheel I got 10.9mpg, and 7000lb travel trailer it was 13.3. This was also mostly mountain highway driving and some forest service road.
The milage just slowly keeps getting better, so I don't think is fully broken in yet.
 
#7 ·
Haven't seen too many (or any) 6.6L owners with Fuelly badges. Just made mine since I have less than 1k on my truck. I bring this up because it always seems like people writing about mileage don't have anything to backup their claims, and the discussions go more in a bragging direction. If you've keep a good log it gives a bit of credence to any claims you make.
 
#9 ·
I started out at roughly 15mpg in town, a few uprades... CAI, Turbomouthpiece (For LLY), 4" exhaust turbo back, and synthetic oil in engine/tranny/rear diff. I raised my intown mpg to about 18 hand calc'd. On the highway I am roughly 20-21mpg unloaded. With a tuner you could get up to about 23-24 unloaded on the highway. Dont go by the DIC in the dash, that thing is way off.
 
#12 ·
Your engine and transmission aren't even close to being broken in yet. Give it some time, and I'm sure that will climb a couple MPG.
 
#13 ·
starspangled6.0 said:
Just about any handheld tuner can add triple-digit HP gains... kinda crazy, but they work.

I've also heard that diesels get better MPG when towing vs. gas engines. I can't say I've personally seen that, since I don't have a Duramax :(... maybe in a few years.
I towed a 12000 lb trailer with intake and banks six gun tuner on level 4 and got 11.5 mpg at 70 mph
 
#15 ·
Just bought my 04 LLY today. She was getting low 20's on the freeway; bone stock. I think I'm going to like this truck :D.
 
#17 ·
If you get it tuned (efi live not a hand held) 22-25 mpg highway empty. My mom and dad took my dmax on a trip and where getting 17 to 18 pulling a trailer with motorcycles in it up to Vermont so all hills to
 
#18 ·
rodcheapo said:
Was that empty? I might have to get a Dirty Max just to save gas......
Yup, at 65 MPH. It doesn't change much at 70, either. I did a little towing today, and my light load (3000 lbs) didn't really have an effect on the fuel mileage.
 
#21 ·
The most I've towed with my Duramax so far is around 5000 lbs, so I have yet to use tow\haul.
 
#22 ·
^^^ 5k is weaksauce, your dmax cant eve feel it :) BTW welcome to the diesel club! I tow my horse trailer about 10k and use tow haul mode , its great and pretty much stops the truck for you. I will be getting efi live this month and one of my tunes will be a turbo break :) !!!
 
#23 ·
have a 2002 chevy Duramax crew cab long bed that is used to pull a 16ft gooseneck trailer to haul cattle and a 28ft camper the truck averages 16mpg but then again it has a 4" exhaust, edge juice with attitude, and K&N filter and always use tow haul when towing and to beat the powerstoke and cummins off the line when they want to race
 
#25 ·
I recently bought an 07 Chevy 2500HD ext cab long box with the 6.6 Duramax and I am only averaging 13-14 mpg (around 15 hwy). I actually checked this with fuel usage and mileage too not going off what the computer says. From what I am reading, that sounds pretty low. Truck appears to be running great just getting bad mileage. Any ideas why? Any suggestions on a modification or chip I could install to boost mileage?
 
#26 ·
I would suggest all new fluids, full synthetic, as well as a new fuel filter and a few bottles of diesel kleen. My 07 diesel is a crew cab long box dually, 200k miles, and she regularly gets 14-17 mpg.

Tuning might help, but that's another 500 -1000 dollars.
 
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