I have over 3000 miles on my truck and the best tank DIC is 14.5 mpg. When doing the math it is closer to 13 mpg. Winter blend makes a difference, but the local Quik Trip has switched and the mileage has not increased. I mostly drive highway and try to keep it under 70 mph. It seems many of the LLY owners report simliar mpg. One of the reasons I wanted a diesel was the supposed better mpg. I was hoping to get around 18 mpg as an average. Granted, driving styles, tires, all make a difference. Not complaining, still better than a gasser. I am beginning to wonder though, if the changes to the Max have anything to do with it. Maybe the better mileages are performance chip related? Not to throw dirt, but many LB7er's write that their mileage improves with age. I would think that as the engine gets older, the injectors and other fuel related components would not increase efficiency with age. Maybe the EGR and CAT have contributed? What do you guys think? Edited by: SonnyBear

My LB7 got 15-17 avg. new.........


once she broke in at 10K I got 18-20 avg..........this is stock.


Juiced and driving normal no real difference.........having fun, 16 mpg all day long.


Winter diesel makes 2-3 mpg difference.





Thttp://www.dieselplace.com/forum/smileys/Big Smile.gifNYEdited by: GMC-2002-Dmax

Since u have 265 tires are compensating the correct % and not backwards?


U are getting more miles than the speedo shows.


My truck is showing 14.9 DIC but some heavy towing/idle time and 500 miles of snow and icy roads in WV.


I've had it since x-mas (5K miles), so all winter fuel, cold gear lube, and it doesn't lock convertor/OD (not sure which) for the first 5-7 miles when cold.

My LLY gets about 14 mpg too combined city/hwy. For a long hwy stretch (2500mi) it got 17.x at 70-96mph unladen.


Yes, I believe the 2WD Manual guys can get 20mpg hwy, but with a 310HP 7100lb automatic 4x4, 14mpg ain't that bad.

I am steady at 16 with an Average speed of 28. So that is a lot of intown with some steady town and a little freeway. I also have 265's on mine and that is going off the DIC so the milage is actually a little better. Now I have to admit to I am driving more like a truck with a diesel vs a sports car. I am sure if I drove more true to form I would be 15 or so. I have 2500 on it right now. I have not done any straight freeway yet but I know that seems to jump right up there on my little freeway trips.





TC

Pulling 3000 lb boat to the lake in hilly terrain 65-70 some 75 my overall is 11.5 this includes launching the boat and some sight seeing in the woods. This mileage is based on the computer reading. In town driving unloaded is 14.


Corsair

My LLY has 410 miles on it, about 25% freeway at between 50 and 60 mph and 75% around town. The DIC shows a 14.5 mpg average but my hand calculation on the second half-tank showed 13.5. I've been doing the "vary the speed" thing even when on the freeway and I am sure this has an effect. I hope it improves by at least two or threee mpg after break-in.

My LLY has 452 miles, with 50/50 city/highway 15.51mpg calculated by hand (DIC doesnt display mpg).

Hummm I think you should have your DIC looked at Hoser, Is the business or Personal turned on?

Had about 470 miles on it today when I filled up for the first time at 3/4 tank down. Probably 50% highway, 50% town. DIC average was 20.1. Hand calculation was 19.75. I'm breaking it in gently and nothing over 65 so far.


This is a stock 2WD, LB, Ext. Cab

I had posted this once before and tought I would share it, this has been hand calculated.


This is the MPG so far, and as others have stated as the miles add up the power and fuel economy seems to be getting better. I must say that my mileage between 1048 miles and 4084 miles were on a trip from Richmond Vermont to Myrtle Beach So. Carolina and back, with a week in So. Carolina all city driving. I drive the truck fairly easy, but there have always been a few full throttle accelerations on almost all tanks after the first 500 miles of breakin.


I do wonder if the operating temperatures of the truck may play a large role in fuel economy as in Vermont my truck only comes up to temperature (210) and once the thermostat opens it runs around 180 deg. where on the trip it ran around 210 on the highway. I guess ill find out more in the next few tanks of fuel back home.


I do believe the type of fuel your using seems to make a difference ( Winter blend does produce less MPG ) and how long of a warm up time has a big effect, but I do feel that these trucks take a long time to get to optimal temp and in cool / cold weather may/ will not get the same fuel mileage people in warmer states are achiving. Just my .02


Sure hope it even gets better, but if it doesn't I'll still be very happy. See Signature.


Fran






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That must be one heck of a ruler and one heck of a stopwatch to measure those Average Mileage and Average MPH figures down to eight decimal places!


Seriously though, some very interesting data. Do you have any data that shows the type of fuel on each of your fills (winter blend, etc.)?


Dennis

Around 3,000 miles on my LLY and DIC says 17.6 MPG AVG, with roughly 70% hwy. I computed my last tank by hand and it was 18.5 MPG (mostly highway at 60-65mph). Driving has been in Feb/March in Toronto area so I assume Diesel is winter blend. Also, very impressed with cold weather starting, just a bit tight for a few miles.

martydma,





I noticed in your signature you have the 28BHS, I have the same trailer in a 2002 model. I have just ordered my new truck and can't wait for it to get here. How does yours pull behind your Duramax? How do you like the trailer? What kind of mileage do you get pulling?


Thanks for all the info.!

My first 500 miles have been 17.2 on the DIC. Havent hand calculated it yet as the numbers I wrote down for my spreadsheet are in the truck.

Update: I just turned over 1000 miles on my truck yesterday. I've filled up 3 times and am just about due for another. I've averaged ~16.1 for all tanks (calculated/actual) with the majority of the driving being city/short trips.


I'm looking forward to getting some highway trips in soon. I am very pleased so far and hope to see an increase overall as the beast keeps getting broken in.

I notice we dont put the Ave MPH on when we put MPG. Usually I am getting 16mpg with an average 25MPH.

I didn't get the steering wheel controls, so I don't have the cool fuel computer in the DIC :(

But on the last two tanks that I've driven the truck without the trailer, I have averaged 17.37 mpg based on my maff skills. Latest fillup was last night: 401.8 miles on 23.132 gallons. Truck has just a tick under 2,000 miles on it now, and is still 100% stock. This is a mix of suburban driving, and highway, driving sanely with the occasional WOT romp :)

I'm happy. I don't know if we are still on the winter blended fuel here in Chicago or not. If we are, then I am expecting to hit 20 empty once we get to the summer blend and I get an Edge and exhaust installed.

I put Cooper tires on within 100 miles. I never checked the pressure they put them at, I assumed they did it right. Well this weekend I decided to check it out. They had it at 45 all the way around, which I think is too low. So, I put the fronts at 55 and the rears at 65. And guess what?????? My fuel milage went up. I am getting around 17-18 with 70% highway and 30% street compared to 14-15.http://www.dieselplace.com/forum/smileys/Clap.gif

Hey jdhankins,


I wish I could tell you how the Duramax pulls my 28BHS, but haven't been out yet. First trip is planned for mid-may for a few hundred miles but I'll probably get out before to test the hitch height and setup (Equalizer). The real test will be 6,000 miles out to Banff and Yellowstone in July. I can't wait to start pulling in the mountains. You will love your truck. The acceleration is amazing and cruising on the hwy at 70+ is very relaxing! Also, very happy with the trailer. My wife fell in love with the interior layout at an RV show in fall of 2002 and you know what they say...the rest is history.

My avg is 13.8 mixed city and highway

Wickedfn4u,


You are absolutely correct, the MPH plays a big role in determining how well you are actually performing in the fuel mileage. You can see by my chart my MPH numbers were going up quickly, due to the long interstate drive, before that was all around home with some warm up time to gewt the frost off the windshield, and with the high idle it sure does burn more fuel and it's not going anywhere!


Just a side note I drive a work truck while on call, it's an 04 Dmax Ally Reg cab. I checked the hour meter on it and was shocked the mileage is 4135 miles the Hours are 185.6 = 22.27 MPH. You can tell once we start it doesn't get shut off untill it's back in the yard. Fran

Well, I got 16.88 on first tank of 70/30 driving. One thing tho, when filling, do you dieselers baby the pump until the fuel is sitting in the neck? I know there is a lot of room after the pump cliks off for the first time. A couple of gallons of room in fact. This was the same as on our gasser as well. Not sure how accurate things can be as with diesel foaming can lead to very inaccurate fills.

A few things I have learned from owning a VW TDI Jetta. On that forum, people have done compression tests and have found that the compression peaks out as hight as 60,000 miles. That is most certainly a very long break in /ring seating period. It may be due to the fact that these come with synthetic oil from the factory, but apparently prior to assembly, the motor is run with dino to simulate breakin, drained, cleaned and then installed into vehicle. I just turned 15k on mine and mileage is still improving.....

1 more thing, on gas vehicles, they have pressurized fuel systems to allow for expansion. When VW puts in the diesel, they do not modify the fuel tank pressurization system. So we do what we call a ventectomy. This basically removes the pressure valve up by filler and allows you to fill to filler everytime. This gave me 1.5 gallons more room and a very accurate fill.

Has anyone ever looked into doing this on the Duramax? Or is it even there to do?

I know when I fill mine that usually the DIC is right on. Filled today and took 19.4 and the Dic said the exact same. I am sure I could top it off if I let it settle, but if you always fill to the "click" your mpg will be the same. If you top one time and not the next you will get a incorrect average.

I usually just fill mine all the way up the filler tube. I like consistency - I usually pay more attention to the trip meter than the gas gauge... and I never know how much fuel I put in the tank is foam, and how much is fuel. When I fill it ALL the way, I at least know it's all fuel.

One thing I should mention also is that I turn my A/C off even though I have it on the auto setting unless it is real warm out. Doing that on my 1500 made a 1.5-2mpg change. Have not gone through the summer with this one yet when I do leave the A/C select on.