hello all, i'm afraid it's my turn to vent. i pull a 24' cobalt boat, with the juice/attitude on #2, and the low boost fuel setting on #4. i cannot, no matter what break 11mpg. if i drive 85, i get 9mpg. if i drive 65, i get 9.5 mpg. this royally pisses me off. what can i do? i also have an egr blockoff plate in a 2005 gmc 2500hd d/a.

the reason this irritates me so, is my old truck was an '03 ctd with a volumizer, mac cold air intake, and dual exhaust that never got below 11mpg no matter what. most of the time towing mileage was 13-15mpg. i cannot go more than 200 miles on a tank while pulling this boat, that maybe weighs 5500lbs full of fuel.

so far this truck is nicer than my last one, nicer driving, quieter, more comfy etc. BUT the one area that i need most, mileage, has yet to be seen. the truck has 4500 miles on it now, and quite frankly hasn't shown me much that impresses me, really other than the allison.

Well first of all you need a signature so that we know what you are running on your current truck. If you have everything the same as far as exhaust, intake etc then you can start from there to try to figure this out. Thanks

test

Quick Question,

blocking off the EGR. Does that make your truck run cooler, or improve the MPG or what?

I think your truck needs to get more miles on it, diesels need 20,000 miles to get broken in, IMHO.

trout

Trout, with respect, your last "quick question" turned into an entirely new question. There is an entire thread on the EGR blocking effort. You might read it before you ask someone else to tell you what it says. That's what we all did.

And I can appreciate the fact that your time is valuable and you'd rather just get a quick answer. That's why there's a search function.

Ed

Trout is right about break-in and improved mileage numbers correllate with this. There is an FAQ (frequently asked questions) over on the cummins corporate website - 5k miles to break-in if towing heavy and up to 20k if lightly loaded. No reason to think our duramax will be that much different.

Many folks complained about initial towing mpg and power over on the lb7 side of the board. Everyone started to realize that the both mileage and power improved greatly at 5-10k miles. Seems like the same thing would apply over here.

- jeff

Trout, with respect, your last "quick question" turned into an entirely new question. There is an entire thread on the EGR blocking effort. You might read it before you ask someone else to tell you what it says. That's what we all did.

And I can appreciate the fact that your time is valuable and you'd rather just get a quick answer. That's why there's a search function.

Ed
"with respect" you sound like somebody with no respect. At least Trout had something to say about steves problem. Maybe you should go back to searching threads, maybe you will see how a discussion works.

Sorry Steve, I have been watching the MPG talk for a while and its my belief that the tires are the biggest contributor to bad mileage along with the lift. I'm getting 15 on the highway unloaded which is 2 mpg down from a couple of buddies with same truck, same town, same fuel but with stock tires. My $ .02

I have a 21ft Mastercraft that weighs in at 5K and I cannot get much better than 8-10mpg running 75mph. Filled up (23.8gals)at 208 miles. I do have 285 BFGs but my LB7 got much better mileage (12-13mpg) towing the exact same set up. It sucks.

Also my fan clutch stayed engaged for 20 straight miles and EGTs averaged 1200-1250 the whole trip.................

I never should have sold my LB7 :(

"with respect" you sound like somebody with no respect. At least Trout had something to say about steves problem. Maybe you should go back to searching threads, maybe you will see how a discussion works.

Sorry Steve, I have been watching the MPG talk for a while and its my belief that the tires are the biggest contributor to bad mileage along with the lift. I'm getting 15 on the highway unloaded which is 2 mpg down from a couple of buddies with same truck, same town, same fuel but with stock tires. My $ .02

I think what he was trying to do was to not let the thread get "hijacked" to an EGR blocker topic. I've subconsciously hijacked numerous threads myself...

As to the effect of EGR, Idid a semi controlled test. I drove a 750 mile round trip route between Spokane WA and Great Falls Mt cruise set at 70 with and without ERG running unloaded. Mileage was within a few tenths either way. Average was just at 18.5, not bad considering I crossed the continental divide along with several other passes. 04 LLY CC/SB/DA 4x4 Conclusion at least for me on the highway, EGR doesn't affect mileage when unloaded. May have an affect in town or with a load.

I have a "bone stock" 2005 Extended cab, short bed. Towing my 25 foot, 6,200# travel trailer I averaged 14.8 MPG. Not towing I get 17 MPG in town and 19.8 MPG on the highway. IMHO the way you drive is the problem.

I am disappointed in my fuel mileage as well. The best I can get is 11.4 mpg. I asked a buddy who got his truck 1 week before me and his read 14.8. The only thing we have done so far is put 285's on the trucks. I am very disappointed so far.

What I get a big kick out of is the guys who swear an LLY gets about 1/2 the mileage of a LB7. Funny how I don't see a bunch of "I get 30mpg!" threads in the LB7 forums. Are automatic 4x4 LB7's really getting over 19mpg highway?

Sheesh...Im getting 14mpg with 33's! Now, if Im on it a lot it drops to 11.5 to 12mpg. If Im 100% highway I can get in the 15's. Not bad for 33's.....

Snapper, is that what you are getting with a programmer?

If he is getting those numbers from the DIC then it is wrong.. If they are hand calculated that is another story.. When you add power and go off the DIC you are never right, no matter if you adjust for tire size and everything else, it will be off...

my truck is bone stock and I get 6 pulling my 9000# 5th wheel, at 60-65 mph, I always got 12-13 with my lb7 pulling the same roads!

If he is getting those numbers from the DIC then it is wrong.. If they are hand calculated that is another story.. When you add power and go off the DIC you are never right, no matter if you adjust for tire size and everything else, it will be off...

I aggree 100% :exactly:

I am going off the DIC for my reading as well as my buddy's. He had never even checked his. Why would there be such a difference for the same truck and same type driving?

I took it to the dealer this afternoon and they are going to hook it up on the computer Thursday to check it out. We'll see...

surf and turf mines in for the 3rd tome for the mileage issue and thay say theres nothing wrong its normal to get that when pulling

What I get a big kick out of is the guys who swear an LLY gets about 1/2 the mileage of a LB7. Funny how I don't see a bunch of "I get 30mpg!" threads in the LB7 forums. Are automatic 4x4 LB7's really getting over 19mpg highway?

I've had 3 lb7's and all of them got over 20 mpg driving "easy". I just don't do that very often.):h
The 3500 lly mpg really sucks, but both my 05 2500's have gotten 18 mpg.

Also, none of my seven trucks ever got any better mileage after break-in.

Snapper, is that what you are getting with a programmer?

Im using my programmer for tire size adjustment and top speed limiter only! No power added until I get my guages! Now, not sure how accurate the DIC is, but in my Tahoe (stock tire size) I could go a week without fueling and was getting 360-370ish to the tank. I go the same amount of time on my duramax between refuels and put the same amount of gas (diesel) in my tank.

That being said, do my numbers make any sense? Or am I a complete moron? :lol:

I have a 21ft Mastercraft that weighs in at 5K and I cannot get much better than 8-10mpg running 75mph. Filled up (23.8gals)at 208 miles. I do have 285 BFGs but my LB7 got much better mileage (12-13mpg) towing the exact same set up. It sucks.

Also my fan clutch stayed engaged for 20 straight miles and EGTs averaged 1200-1250 the whole trip.................

I never should have sold my LB7 :(

I don't know why there is such a wide discrepancy in mileage. I get an honest hand tested 13-14mpg pulling 5k-6k (23 foot boat or 2 horses in trailer take your pick) at 75mph and a touch more if I leave my lead foot away from the throttle and let the cruise earn it's living. I also have 285 BFG's.

I can't imagine dropping down to 8-10mpg, I would think I had a fuel leak or something else wrong.

.

I am also having some of these problems. This is actually my first post here too. I have a completely stock 05 duramax quad cab short box and have been averaging 14.2MPG at the highest. It's lower when I tow my 23' boat. I am around 3000 miles as well. Is it too soon to be towing?? For the last 1000 miles I have been very light on the pedal and tried to beef up the MPG. Just when they start to go up, I tow my boat, take it off and the MPG is still screwed for the next week. I am considering taking the truck back to the shop after a few "general transmission" faults popped up and disappeared. ANy help would be appreciated.

I jumped about 1.5-2mpg after I hit 1500mi.

i get about 8 pulling my 14000 fifth wheel and about 13 to 14 running empty.

I am getting just around 18 mpg empty in town. Don't know about towing haven't done any just yet but this Tursday will be my first tow with my 3500. Got about 2400 on her.

I am pleased so far getting much better mileage than the 6.0 I had in my 2001 1500HD. I could go 300 miles on a tank of 92 liters (Not sure how to convert to Gallons) and I have gotten 675 - 700 with the DMax and it not broke in yet.

I seem to get the same milage with stock, 40hp or 65hp preditor tune. The next thing to try is egr and cat removal. Its still not clear if that will help but you would think it would have too. I also want to look for a different tire after the bfg's wear down, something that looks good but gets good milage any suggestions ?. I also think alot of the guys that are getting the good milage are 2 wheel drive + low to the ground.

I've only got 3300 miles on mine, pretty much sits in the garage. But running empty 60-65 I'll run anywhere from 18 - 20 hand calculated. Wind and speed are big factors. City driving I'll range anywhere from 14-16 depending on how heavy my foot gets.

Pulling 7,500lb TT running 60-70 in some really up & down hills with a 20 MPH cross wind I'll get 10-11. If I get on the flat and no wind it'll bump up to 13. Big ole air dam back there.

The spped you drive is also key, running the rpm above 2200 kills the milage. Here in california if your not doing 80 you will get ran over.

Just my experience with my old LB7 vs my new LLY.

LB7:
Unloaded 17mpg to 19+mpg on commute (80% highway)
Towing 11K 5'er 8mpg in mountains 10mpg-11mpg anywhere else

LLY:
Unloaded 14mpg - 15.5mpg on commute
Towing 11k 6mpg in mountains and 7mpg to 8mpg anywhere else

Both trucks stock only difference is LLY still has only 2500 miles so hopefully some improvement in the future (although my LB7 was better from the git-go!)

We just returned from an 1,110 mile trip towing the monster camper (35' ft. long travel trailer, about 9,500 lbs. loaded). Last years trip the truck was bone-stock, with about 3,000 miles on it. We averaged just under 10 MPG as per the DIC. This years trip was done with the same trailer and driving style/conditions. The truck's Predator was set on the 65 RWHP tune, and I installed the 4" Corsa just before we left. Hand-calculated, we averaged 13.5 this time around. The truck now has just over 15,000 miles on it. I'm sure it's a cumulative effect from the mileage, exhaust, and programmer, but it was a noticeable improvement. We cut out an entire fill-up, and I pulled up the driveway with half a tank. This truck only gets better. Had a Powerstroke parked next to us, and another Duramax on the other side. The PSD was only getting about 11 MPG with a Superchips tuner and the 5" Summit exhaust. The guy in the LB7 was pulling lighter, with no mods, but still getting over 13.

Mark

I posted this a few weeks back. My mileage got better after about 7,500 miles, and the exhaust has helped as well. For the power this truck puts out, I'm pretty happy to be getting about 18-20 empty. 30+ would be nice, but it's unrealistic in a 7K lb. vehicle. Mine's a 4X4 with the stock 245s on it.

I would love to see 18-20!!!
My truck has almost 8,000 miles on it now.
I run a predator on the 65hp setting, tires are 285s, and I did use the predator to calibrate for the tire change. The speedo now only reads 3 mph slower than my GPS..
DIC reads 16.5-17 on average. Best hand calculated average driving (empty) has been 14. My daily commute is 70% highway miles.

The truck even has a bed cover on it!

I'm highly unimpressed by milage thus far.:(

I have a bed cover on mine as well. I do drive with the instant fuel economy reading displayed on the DIC, and try to make minor adjustments on the fly to maximize my MPG readings. This time last year I was pretty depressed with the mileage, but it did improve.

i have a boon stock 2500hd crew cab 05 with 3300 miles. i am getting 18-20 mpg interstate and about 9-11 mpg towing a 7000lb tt any wheres from 65 to 72 mph. i hope i get better fuel mileage than that towing -:t

I have a bed cover on mine as well. I do drive with the instant fuel economy reading displayed on the DIC, and try to make minor adjustments on the fly to maximize my MPG readings. This time last year I was pretty depressed with the mileage, but it did improve.

Do you guys think the bed cover helps on mileage?

Bone stock brand new '05 4x4 reg cab, long box, Leer shell I've averaged 11.5mpg with 50/50 split towing and empty in the Rocky Mountains with a grand total of 2600 miles on the truck. Low mileage towing was 8.2 (heavy head wind and 22' camp trailer loaded), high 9.8. Usual empty was 12 something and a high of 17 on a 120 mile blast. So far not much better than my '93 454 suburban. However, driving in the West I haven't gone under 70 ever. Can't keep it under 2200rpm when it tachs at 2500 @ 75 or so. Love the truck for sure but really hoping for improvement in mpg.

i don't know if i've said it before or not, but i don't drive this truck even remotely hard! 60-65mph i get 18-19.5mpg unloaded. even with the big tires! BUT for some odd reason it absolutely drinks fuel when loaded. i'm beginning to wonder if i never noticed this on my last ctd because it held 10 more gallons of fuel!

i looked into cold air intakes and other mods with the intention of getting some better mileage, the best i came up with is using an LB7 front pipe, an economical chip, and hoping for the best!


transferflow has my undivided attention right now, this small tank sucks.

steve, myself and others have had great luck with a modified S&B box. I hope I didn't post that here already. e-mail me if you decide to go that way and I will show you my mods.:D Also check my posts on the overheating thread for intake air temp drops with this box.

I don't know why there is such a wide discrepancy in mileage. I get an honest hand tested 13-14mpg pulling 5k-6k (23 foot boat or 2 horses in trailer take your pick) at 75mph and a touch more if I leave my lead foot away from the throttle and let the cruise earn it's living. I also have 285 BFG's.

I can't imagine dropping down to 8-10mpg, I would think I had a fuel leak or something else wrong.

.

At 75mph on my Attitude (corrected for tires), cruise set, I averaged exactly 8.7 mpg towing my boat to Arkansas. This was hand calculated and mileage was adjusted 7% for the tire difference. This is I-40 between OKC and Ft. Smith which is relatively flat and this particular trip the wind was non-existent since the temps were in the 100s.

I have been making the exact same trip for well over 15 years in all kind of trucks and this one is by far the worst. Even my 5.7 vortec gasser averaged better mpg. IIRC the same exact trip in my 02 LB7 two years before, same tires, same load, same time of the year, same speed, I ran 12mpg.

I have yet to break the 14mpg mark after 20k miles. I commute 80 miles of interstate a day at 75mph, 2250rpms, with a few miles of city driving. I fill up consistently (the same way each time at the same station) at 300 miles and usually take 23 gallons.

I keep a log of my hand calculated and adjusted mileage and my mean mpg over the last 20K is 13.37 unloaded and 9.8mpg loaded (same load every time).

Over 89k on my LB7 my mean MPG was 15.8mpg and loaded 12.87mpg.

I think my fan has a lot to do with the decrease in MPG. Often times on my run home unloaded the fan will engage completely for a few minutes. I would say 90% of the time on my trip to and from AR the fan was engaged...............probably 40% at the first level of engagement and 60% wide open, can't talk to my wife, full on engagement. I actually recorded a 20 mile stretch where the fan was fully engaged and engine temps were well under 200. By contrast I cannot remember my LB7 fan being so active or loud. Hopefully our members will find a solution to the OH issue and we can find a way to keep the fan from engaging so frequently. I am quite certain if the fan is not engaged so much the mileage will improve.

Slow Down!

33,000 miles on stock LLY and I commute every day, 80% on mostly flat highway at around 65mph. The truck consistently get's between 19.5-21mg per tank as calculated by DIC (but I don't drive very hard). This hasn't changed much over the life of the truck or even in winter. I noticed mpg does drop significantly with short trips, stop and go or aggressive driving.

I towed my 6k pound 30ft TT 6,500 miles last July out to GNP Montana, Yellowstone and Black Hills SD. The whole trip averaged 12.4 mpg. Direction of the wind had the biggest impact on mileage. I know some are dissappointed, but I am one happy camper when it comes to fuel mileage since I was used to my Ford Expedition at 14mpg (solo) and 6-8mpg (towing the same trailer). I rarely passed a gas station in those days.

33,000 miles on stock LLY and I commute every day, 80% on mostly flat highway at around 65mph. The truck consistently get's between 19.5-21mg per tank as calculated by DIC (but I don't drive very hard). This hasn't changed much over the life of the truck or even in winter. I noticed mpg does drop significantly with short trips, stop and go or aggressive driving.

I towed my 6k pound 30ft TT 6,500 miles last July out to GNP Montana, Yellowstone and Black Hills SD. The whole trip averaged 12.4 mpg. Direction of the wind had the biggest impact on mileage. I know some are dissappointed, but I am one happy camper when it comes to fuel mileage since I was used to my Ford Expedition at 14mpg (solo) and 6-8mpg (towing the same trailer). I rarely passed a gas station in those days.

I still wonder why they are so different. Your 12.4mpg towing 6k through hills is about the same as me getting 13-14 or so flat ground same weight. But it sure seems some trucks are way way off the mark.

.

Slow Down!

I'm driving the speed limit!

Any slower and you get run over......................

My truck also gets 19-19.5mpg driving 68 or so. Hand calculated and DIC was right on. That was with the 245's on it. It got 14.3mpg pulling my 4000Lb boat at the same speed. I've got 285's now. Not sure what to expect.

I live in Phoenix and I was getting 17-19.5 mpg before the lift and tires. I now get 13-14.5 mpg(corrected) as a result of the tire size. I have a 20' tt that I have towed both stock and with the lift. Stock 10-12mpg while towing. Now I get 8-9.5 mpg consistently towing the 5500 lb tt. I usually cruise at around 75 mph on the interstate while towing. The stock 373 gears give a speed around 65 mph with 2400rpm - OD off, for the hills.

I live in Phoenix and I was getting 17-19.5 mpg before the lift and tires. I now get 13-14.5 mpg(corrected) as a result of the tire size. I have a 20' tt that I have towed both stock and with the lift. Stock 10-12mpg while towing. Now I get 8-9.5 mpg consistently towing the 5500 lb tt. I usually cruise at around 75 mph on the interstate while towing. The stock 373 gears give a speed around 65 mph with 2400rpm - OD off, for the hills.

If that was me, I would have to go back to stock size tires, considering the difference in mpg.):h