Well first off I must say that I'm new to the forum. I just purchased my lly d/a on june 5. I wasn't planning on buying but the dealer shot me an awesome price. I used to drive an 01 ford powersroke crew cab with the 7.3. But I sold it a couple of months ago with the plan of buying a new truck in the fall. Well fall came a little earlier than i expected. Any way My fuel milage is crap compaired to my old ford. I drive between 80 and 83 on the intersate. And right now I averaging around 13.5 according to the dic. When I fill up I'll calculate manually to see how accurate the dic really is. My ford generally averaged around 15.5 to 16 going that speed. I did run the 80 horse superchip on the ford so that might have helped a little. Any way I was told that it takes a few thousand miles to start seeing better fuel economy. I have just over 600 on mine and was just wondering how many more I need to start seeing better milage. I plan on doing some sort of chip when more options become avaliable.


sorry I was so long winded but any info would be appreciated





thanks Justin

Justin,


I posted a question about fuel mileage a few weeks ago when I picked up my new 2500 HD LLY. After reading the answers to my question and the other fuel mileage threads on the board, I have come to the conclusion that either peoples driving habits or variations in trucks are causing huge fuel mileage varations not break in. I am not sure that 13.5 mpg at over 80mph is really all that bad. I am betting that where people are driving (crowded roads, passing, stop lights) have a lot to do with it too. My 73 year old mother gets a solid 1-2 mpg better than I do no matter how hard I try.


I get 22-23 miles per gallon driving 45-55 mph on local two lane highways. 16-19 mpg on local paved roads, a very poor 6-8 mpg on two track gravel/dirt(expected). The DIC is accurate to 1/10-2/10 of a mpg so far. I have 4-5 tanks of fuel through the truck. There aren't any interstates here and I have never gone above 55 mph as the truck is new and I am going beyond GMs recommended break-in period (500 miles under 50mph, no towing before 1000 miles)because I want the truck to last. My mileage has been in this range since the first tank.


The rear end in the LLY with Allison heavy duty package has extremely close tolerances and generates extreme heat in break-in. It seems a lot of people are towing at 80 mph there first weekend or chipping the truck with 11 miles on it. You do that and your truck will never break in or get the best mileage.


I bought the truck so I could improve on MPG while towing and to withstand long mountain tows with reliability. My gas truck got 6-7 mpg. Towing was destroying the truck very quickly. I think I got 8 mpg once with a 30mph tail wind going 60mpg. I am hoping I can come close to doubling that at 60 mph. If got some of the mpg reported(see towing thread) on this board, my truck would be back at the dealer. Try driving a empty, flat stretch of road at 55 mph. Reset the personal average mpg on the dic when up to speed. If after 20 miles you are not averaging over 20 mpg, I would say there is a problem.

I agree with YooperSam. You can ignore most of what is posted here about MPG. It is nearly entirely dependent on the driver, not the truck. I have 6,000 miles now and absolutely no change in MPG since it was new. I'm not unhappy with the mileage. I can always (as can everyone) get a couple more MPG by judicious control of the right foot.

I am pushing 2K miles since I picked it up 3 weeks ago. Combined city and freeway driving, my first few tanks were at 15.3 average, manually checked. Over the last two tanks it has steadily gone up. I am halfway through a tank right now and the dic shows 17.2. It is within 2/10ths of manually calculated, so far. I drive the same route each day, same time of day. The weather here has heated up quite a bit since I bought the truck so the ambient temps are not helping the mileage. On the freeway, I set the cruise at 75mph, minor up and down grades. Air is on in the afternoon commute home. My commute is 22 miles, 12 city and 10 freeway.





Bone stock 2004 LLY 2500HD.

You will definetly pick up, about 2000 miles and it was like a new truck damn near 21mpg with the stock 245's at 73 mph average straight highway.

Might as well throw my .02 in. I just go back from an 1800 mile road trip from Utah through reno to California and back through Vegas. I run 285's on mine with no other mods. From Salt Lake City to Reno I got 13.1 MPG calculated manually. At this time the truck had about 2000 miles on it. I averaged about 81-82 mph on the freeways.


From Reno to home I got about 15.5 mpg. After this road trip I will say that SPEED is the biggest influence on mileage. If I travel at 81 mph on the freeway I'm going to get 13 or so, if I drop it down to 75-77 I will get 15 to 15.5 and so on.

well i just did a 1650 mile round trip to N.C. my truck was loaded with file cabinets and furniture. intow was a 20 foot trailor with a 92 ford sable. in that car was a bunch of cloths. andi calculted all my gallons and miles on a cheese-it box and i got 15-16 mpg. the truck rarely got over 2000 rpm's and we cruised at 65-70 mph all the way. some times 50-55.


with a empty load i got about 17-18 mpg going 70-75 some times 60-65. i was towing the empty trailor.


it all depends on how heavy your right foot is i gues.

I just filled up fpr the second time. This tank was all city driving and I got 17.4. I am very pleased with that. I wo't get any good howay numbers it July whe I go west.

Greg

I just took a trip with my new CC to ny and back from mi. Since I've gotten the trip I'm averaging 17.5 mpg. I've got 1600 miles on it, and only the first 100 of that was city/slow highway, all the rest at about 75mph.

Definitely depends on the foot. When I go 80-85 I get 16.5. If I keep it under 70 on highway I can get 19. Around town 14.5 to 15.5. It has been pretty consistent since new and I now have 2,500 miles. I have auto climate control and the compressor is almost always on. Doesn't matter, mileage has stayed the same with or without. By the way, since the first mile my DIC has been consistently 1/2 mile per gallon lower than manual calculation at each fill up. I mean it has been EXACTLY off that amount every time. Pretty interesting. Hope that helps.

have had my new d max for 5 weeks. over1600miles .one way to work 18 miles .combo of driving worst mpg 16 best tank 18.5 averagefor all miles 17.8http://www.dieselplace.com/forum/smileys/Approve.gif.just love power and mpg compared to 6.0i had

Mine has 2200 miles on it, has been averaging around 15 mpg around town on the DIC, went on road trip got 19.5 mpg on DIC, I had to add in the extra 8% because of the tires so it was getting over 20. I'm happy so far but would like a programmer for some more power.

I just got back from colorado in my new lly, I drove moderately consevative and got 19.8 mpg, on my trip up there my DIC said I got 16.8. The truck now has 700 miles on it.

I get 12.5 NO MATTER WHAT! I haven't reset my DIC since I got it, and It's still at 12.5. At 75 mph my instant reads about 14 mpg. I must have a bad one. I do have a Dually crew cab and maybe some of you have a regular cab with a ZF tranny....

Mine got 16.5 average on the dic for the first 7,000 miles (never reset it) and when hand calculated at fills ups it was always about 1mpg lower. Last two trips I reset the dic and supprised got 18.5 on the dic at 75 with 600lbs in the bed! It does seem to run stronger than when it was new. Installing nictane hopefully this weekend and going to (delvac 1 or truck/suv) synthetic at 10k (real soon). Did change front and rear diff's at 7k to mobil1 syn.

14.9 mpg averaged over 5000 mi, 100% stock except 265 revo's, before exhaust, with Amsoil synthetic bumper to bumper. I wonder about some of these claims, this is my second Duramax and the best single tank(stock) I have ever seen is 16.5mpg empty. The worst tank is 9.5mpg with a combined gross weight of 13,440lbs. Looks like most people take the max reading they see on the DIC and convey that as their average, does anyone use a longer sample to calculate average mpg? Does anyone have 15k-20k mi worth of data?

My 1st Duramax was a 3500, D/A, 4x4, CC. That truck had ~18000mi before it finally loosened up!Edited by: RaceHemi

I am new to the forum today so bear with me if I repeat someone else. I have a 2003 SIERRA 2500HD CREW/4X4 STOCK TIRES 245's with 22,000 miles and I am getting consistently 17.5 mpg not towing about 50/50 city/highway. I am pretty happy coming from a gas engine to this, especially with curret prices. Although these are good numbers I frequently drive a dodge cummins 3500 4x4 at work and it is getting close to 21 mpg. I frequently checked consumption when my dura was new and I have improved about 2 mpg since then.

Thanks for the info. I guess I'll just have to slow down if I want the better fuel milage. Hopefully putting the exhaust and a chip will help improve the milage. Also thinking about 265's. If that don't help, I'll be pretty dissappointed that it won't get the milage that my 01 powerstroke did. I also wish when people are talking fuel milage that they would list the speed that they drive when they are getting 19 to 20 miles per gallon. I know that there are a lot of variables in the milage game. But I'm just looking for ways to make mine better. Thanks again for the info.

You have more HP and torque than the power stroke so it might burn a little more fuel. I don't think any of these trucks a completly broken in yet. Mine just keeps running better and better with 6000 on it. That tells me that it isn't broken in yet. Once everything loosens up a little I am sure it will get better mileage. I would say about 10,000 it should be preaty much broken in and the fuelemileage would probably be at its best

well I'm not really being fair. the powerstroke had an 80 horse chip. Before the chip it was getting around 13 to 14 at 80 mph. So that brings the horsepower from stock of 250 to approx 330. And torque from 505 ft lbs to 645. So that's about in the area of the dmax. So that's why I'm saying if I chip it and put an aftermarket exhaust on it the milage should improve. It seems to me that to a point more hp equals better milage. I'm sure that putting a few more miles on it couldn't hurt either since I only have 700 on it. I'm not trying to start a Ford vs Chevy thing here either. I love my chevy but I'm just looking for advice and answers