Alright ive seen some pretty bad mileage threads showing up from time to time. But this one is just aweful.

You can see in my sig what type of truck setup etc that I have.

I have the Edge / Juice and always leave it on Level 1 (except for engine temps <177 degrees then its on 0 because it knocks WAYY too much at loads >35% for my liking!)

I cant figure it out, changed air filter, Switched over to 5w-40 full Synthetic Shell Rotella-T, new fuel filter, new tranny spin on filter (all has <500 miles).

This past tank I hand calculated and got 265 miles to 1 tank (24.3 gallons) that comes out to ~10.91mpg. :eek: I know this is a big truck but how can the mileage be soo BAD? Earlier this summer I was averaging ~17mpg in town 22 on the interstate.

The only thing I can think of is on my way to work I can drive ~15 miles and never make it above 175 degrees.. the Average speed is 50mph and its a 1,000ft drop in elevation.

Could these low engine temps be causing it to run rich thus decreasing fuel economy considerably?? In the morning I plug it in and let it warm up to ~120F before heading out.

Truck has ~27,000 miles on it.

Help!

do you have winter fuel? these things also get less mileage when it is cold. you may have an egr problem also. our 06's are notorious for this, mine has already been replaced, and it was at 26,000 miles.

don't feel to bad I just filled mine up and it was a whopping 9.6 mpg hand calced.I've had a 02 /03/04/06 demax the 03 got me the best mileage but i have a hard time believing more than 17mpg I want to know where they sell the 20 plus mpg calculators it make me fill better. I'm sure winter fuel does not help. so lets get rid of winter and it will all be ok just my 2¢

You have definetly got something wrong Enigma.
Maybe try the dealer with the complaint and see what they say. Try running without the edge and see what happens. Maybe that's your problem.

Also do you have a winter front on??

How much do you idle the truck?

Sounds extremely low. The worst I've been getting in the winter is about 15mpg.
If you said 12-13, I might think that was ok with bigger tires but it sounds like you have another issue.

285's will hurt the mileage.
But to me, we need to look at that temperature issue. What temperature is it there? Are you running a winter front? Why is the engine temp that low?
Engines are more fuel efficient when the operating temperature is higher than what you posted.

I have been running around 11mpg when it's really cold, with the top winter front on. With the extra idle time when it's cold it's about normal. When it's not -20 I go up to 13mpg/ Far cry from the 18-22mpg I was getting in October. All hand calculated.

I think I might start keeping track of my distance traveled / engine hours as well. Could be interesting comparing winter to summer that way.

wow even with winter fuel thats still real low....go the the stealer

Ya, but I figure with sitting 20-30 minutes a day on high idle that will eat up the fuel. When it's really cold I warm up atleast 10 minutes. After reading all the high idle worries I kept meaning to turn my high idle off, then I read the latest post that put those worries to rest.

Are you filling up at different places or the same one? It seems like a different places can cause changes in mileage. I get around 14-15 and I have whats about = to a 33" tire.

My truck does 12 mpg at this time of year....

I run my edge on 4 and have 235 on mine and iam getting 16.5 to 14.5 with mine

So I'm not crazy then. My Duramax was getting 10-11 on the highway. No codes, ran fine, just crappy mileage. I put the edge juice and attitude on to see if it would help. I leave it on level 3 all the time and now I'm getting almost 14 hand calculated. That's a little better, but not what I expected from the truck when I bought it. I hope it gets better with the summer fuel.

You should definately be getting better fuel milage than that

9-12mpg here, WTF???

I will agree that I have seen some very odd fuel mileage too. Granted I have been driving around with my plow on the front of my truck the past week or two. i havnt been idleing in excess at all. and havnt had a heavy foot or gotten speeds over 60 MPH. I have been avg. between 11-12 with plowing thrown in to 13 with no plow and just back and forth to work. As much as I love the snow now for the money factor I am ready to get summer blend back b/c this fuel mileage SUCKS!!!!!! My last 7 tanks have been under 14MPG and only two of those tanks had the plow on the truck. I have been filling up at the same station each time and driving the same pretty much each time. I will say it has been quite a while since I put any type of additive in the tank. I just picked up a bottle of Power Services tonight to toss in so maybe that will help some.

Something is wrong! I have the identical truck and I get 20 to 22 MPG on the highway! I'm running an Edge on level 3, boost 5 and I have no problems including pulling the trailer you see listed in my signature! You've got something wrong! Sorry!

Mine is about the same, 10.8 and it's very consistant hand calculated. It does'nt matter with the cat on or off, S&B filter or stock, EGR working or not, winter cover on or off it still stay right there at 10.8.

I came to the conclusion that I will have to live with it because it's a big truck. I'm just glad I'm not alone.

I just can't figure what the 17 to 20 MPG guys are doing different, and why there could be so much difference between trucks.

Thanks for listening KDS

Mine is exactly the same....10.9 hand calc'd. I have my Hypertech set on Stage 2. I don't know if they have the winter fuel in NC or not, I suspect they do. I do not idle much at all and still have the stock (245) tires. I was previously getting 17-20. I'm suspecting the EGR is the problem.

The number one contributing factor of bad mileage in most cases is driving habits. People think they are not heavy footed because they stay below 100 mph, how you take off is the worst culprit. Now I have read a couple of posts that say they never get above 60, there is part of the problem right there. My truck with 3:73 rears best mileage is @ 75 mph. Getting up to speed just take it easy, people love to see that black smoke roll, but think or that black smoke as money.

If you look at my sig my truck is moderately modified, and I still get 20-21 on the highways @ 75 mph, and it drops to 16-17 running around town. Mileage was terrible until I got 50k miles on it, and once that point was hit it gradually got better. You have to understand, these motors are million mile motors if taken care of and built to be able to do that, so it takes a while to break them in. If you abuse them they won't make it, but if you take care of them, they will be the last truck you buy, unless you hotshot for a living. Just my thoughts, don't mean a thing to most, but I thought I'd throw them out there.

Mine is about the same, 10.8 and it's very consistant hand calculated. It does'nt matter with the cat on or off, S&B filter or stock, EGR working or not, winter cover on or off it still stay right there at 10.8.

I came to the conclusion that I will have to live with it because it's a big truck. I'm just glad I'm not alone.

I just can't figure what the 17 to 20 MPG guys are doing different, and why there could be so much difference between trucks.

Thanks for listening KDS



That's exactly what mine is getting around town here........10.77 or so MPG......I took one long highway trip and got 17, but my driving is mostly town, so I suppose it is what it is. It does this with or w/out the PPE and with or w/out open exhaust, but I did put on the 285's right after I bought it, so I'm sure that did hurt it some, along with this winter fuel....We will have to wait and see.

I think you are fine. I'm in the same boat. Winter fuel + No warm up due to elevation change during the morning gives horrible mileage. The summer time mileage is alot better!

Seems like something might not be right about your truck. The worst I ever got even with winter fuel was around 12 MPG and that was towing a camper. Best I ever got was 22.8 MPG, hand calculated. Just checked mine yesterday and it was about 17 MPG. Of course that included about 5 minutes idle time at each start up and mountainous driving, but on the open road at speeds around 55 or 60. Do you let your truck idle alot and do you have a heavy foot? Just little minor things can make a big difference.

18.4 mpg last check by hand, I have the Edge J/A level 4 boost 4 I warm it up, but it's not cold in Texas.

Dane

[quote=BIGR;2431815]Seems like something might not be right about your truck. quote]

My question to that, is where would you start to look? The oil level stays fine.........it doesn't seem to smoke very bad at all........????


I've asked the dealer and they said some get 10....some get close to 25 or so MPG.....

It's not that I get mad because I get 10 + MPG, it's just that these things seem to be not at all consistant, where as the gassers seem to all be between 10 and 13 MPG........just an observation :D

[quote=mfbarnes;2431694] My truck with 3:73 rears best mileage is @ 75 mph.

I'll guarantee you would get better mileage in the same conditions at 55. I certainly agree with your other points. I once took a trip to Illinois from Indiana (flat) and drove 45-55, just keeping the torque converter locked up in 6th gear, 300+ miles and got 23.9 miles per gallon hand calculated totally stock including 245 tires. When I drive 75, I've gotten between 20.2 and 16.7 depending on wind conditions. I've been nearly coast to coast (Va Beach Va, to Idaho border through Rocky Mtns.) and wind is a huge contributing factor with these trucks. I've been in conditions heading West into a head wind and turned around on the return trip the same day with the same wind at my tail and have improved over 4.5 miles per gallon!

Something is wrong! I have the identical truck and I get 20 to 22 MPG on the highway!
Me too (at 65mph) - checked several times, and it's accurate. My truck is completely stock, except 265x75/r16s or 16x7 wheels (which do NOT hurt AT ALL)
Could your DIYC be screwed up? Something is wrong, badly wrong.
No offense to anyone, but I'm with mfbarnes 'The number one contributing factor of bad mileage in most cases is driving habits. People think they are not heavy footed because they stay below 100 mph, how you take off is the worst culprit.'
I know is tempting to use the acceleration capability -- but with driving habits, you take your choice: performance or mileage. Try keeping the RPM under 2000 on take off.
btw, your truck will last longer, too.

As far as mine goes, I always hand calculate it. I've never even seen on my DIC where to check MPG, so I wouldn't know how anyway...lol


I don't baby it, but I don't drag race it everywhere either. I love the truck........simple enough :D

idling,stop and go, 285's will kill your mileage and then add for winter blend fuel. i average 14-15 but i am lucky all i have is 2 stoplights to and from work.

Presently I'm at 9.2 mpg. I don't drive it crazy, the roads are too bad to do it. What it comes down to is winter fuel. These trucks really hate it. Some places blend with #1 and some places blend additives into #2. In the end, the fuel has less BTUs. These trucks really don't like the cold weather either. It was -6 F this morning. I quit using high idle because I can't keep tranny cooler lines it also, anything below zero and it pukes fluid from the crimps on the lines or the seals in the fittings.

Ya thats crazy.

I usually plug in my truck to bring it up to operating temp faster. Let it high idle for maybe a min or so at the most (till it gets up to 105 -110 degrees F) and then take off and drive really lightly it will take me about a 1/2 or so to get up to 50mph and then maintain that speed until i get to work with the exception of 10 or so lights.

Oil level was just changed not too long ago and I even put 5-W40 synthetic in there to see if that would change anything.

No luck, what are the symptoms of a clogged EGR?

Also, the Edge / Juice is setup to clear all trouble codes on startup because I have the turbo timer setup on the truck.

sorry about your luck. im not sure why mpg are so diff i get 20 to 21 on the highway almost always around 75mph unless real windy. I was just pulling a 4500# trailer with a 11,500# mini excavator at 63 mph cruise and was getting 12.5 hand cal. pulled it about 30 miles. highway filled up right before to the neck. and just filled again when i got back.

I have an 07 cc LBZ . I generally do much better but I tilt the board to favor mileage when commuting. Truck is stock:245/75-16. Synthetic oil everywhere but trans.11k miles. GMC w/ top winter cover but temp here has been between 12 and 50 degrees.My commute is all highway 25 miles each way.I only let the truck warm up until the voltmeter goes to 14 volts which indicates I'm running no glow plug or warming grid in intake.Then I *****foot it w/gradual acceleration until I hit 60 mph .Then cruise control It @ 60 until I get to work. Pretty boring huh. I'm @ 18 to 19 on the DIC in the winter.If I go to 80/20 Highway/city mix I move down to about 17 mpg. Oh yeah ,I forgot to say I have a hard tonneau cover.

Theres no such thing as a free lunch

I was averaging 15.5 mpg on my 07 classic. Installed Kennedy Diesel's custom tune and got 2 mpg more. I figure it will pay for itself in 2,000 miles at the current cost of diesel

I've been brainstorming on this topic, because I'm in also in the club where I'm seeing about 15mpg max and often in the 12-13 range - I do however have a canopy but usually only have a couple hundred lbs of tools in the back. Anyways, it seems like a lot of guys that are getting 17-22 mpg might live in flatter or less populated areas. I can't drive 5 miles without considerable elevation change and traffic, and am basically up and down hills for my entire typical 50 mile commute, and/or in slow and go or stop and go traffic on I-5. I imagine I'd be seeing much better mileage on flat open highway, but there is simply no such thing out here, at least for a 150 mile radius around my house.
Anyways, just a thought. It seems like 10ish in a cold climate, short commute, and extreme elevation change might really not be that bad. It seems these things like to get pretty warm before smoothing out. JMO.

I was doing some digging and found something kinda interesting. Ever since I installed the fingerstick my mileage has been kinda odd. The tires and lifting the truck up didnt really effect anything. I got the same actually .4 better on a trip up north and was pretty much the same city and city hwy mix. Ever since the fingerstick install its been off. Is there a tie between the two or just a coincidence?

Lately I have been using my truck to drive the kids to school, 15-30 degrees in the morning, 2 miles each way and I have to get up to 60mph quick just out of my driveway. I let it idle until the fast idle kicks on and then take off ~one minute usually. Last tank where I used the truck for mostly that and some city driving was 10.9mpg (hand calculated) oddly enough.

Last week I loaded up my 26' 8500lb enclosed trailer and race car and towed it to Detroit (560 miles) and got 11.1mpg @ 70mph and it was pretty damn cold out. Dropped the car and trailer off, drove 330 miles to Chicago and 550 miles back to Knoxville unloaded with 4 people in the truck plus a few hundred pounds of stuff I didnt want to leave in the trailer and got 17.6mpg empty @ 75mph.

I have got as good 12.5mpg towing and 19mpg empty in the summer so it really depends what you are doing with the truck. I dont think mine has ever been floored in 20K miles except when towing and its 100% stock.