2004.5+ LLY Duramax Fuel Economy Poll

[AKMark]

05 LLY, CC, LB 94K miles, 15K hours, unknown age of injectors, runs great though.

In Alaska with temps in the -20 range, 15 driving approx 14 miles one way twice a day every day. (56 mph, if I drive 60 this drops to 13)

17 over a 85 mile drive with 3 hills over 8 degrees of upward angle. (67 mph)

This is with #1 Diesel, mixed with 2 stroke oil.

I haven't taken it on any longer road trips yet, and unfortunately all of our roads out of Fairbanks will encounter big hills.

[gary_lucas]

Had the truck for almost a year now, put about 12k on it.

Overall thinking it's a great truck, but the fuel economy is less than I hoped for.

My last set of numbers put me in the 14.2mpg range with mostly city driving unloaded.

When I got the truck last year it had:
* Modified exhaust (Not sure what it is, going to find out tomorrow).
* Edge Juice with Attitude.
* p265/75's

I've removed the attitude module this evening for the first time. I had a bakflip installed this past week and I'm going to get a Kennedy tuned ECM for our trip down to Las Vegas next month. We'll be hauling a 3200lb trailer so I'll get a good idea of the mileage at that point.

My understanding of how to drive with fuel efficiency in mind basically starts and ends at takeing it easy, don't floor it to get up to speed, Keep it at the low end of the speed spectrum (IE on the highway keep it towards 55 rather than 70 if at all possible...)

When the current 265's start getting old I'll probably replace them with the stock 245's and hope to see some better fuel economy.

[gary_lucas]

Followup, just drove from Vancouver BC to Las Vegas Nevada and back up the I-5 in California.

Combined average of about 17.5MPG the whole way. I was towing a 3000lb trailer with a really low profile (low wind resistance).

I was getting close to 19MPG on the I-5 on the way back, going through the mountains brought it down to 17.5 approximately.

[AKMark]

First long road trip with my 05 this last weekend.

734 miles driven (per gps). I have an 80 gallon external tank in the bed that keeps the main topped off. It took 35.7 gallons to top off the external after we got home and I confirmed the main was full.

20.7 mpg, I drove 67mph (per gps) except for about 200 miles on the way back when I stepped it up to 72mph to keep up with a convoy of friends.

Considering my motor has over 16K hours on it, I'm happy.

[dfenze]

04.5 LLY with 110K miles. When new I was getting 18-19, no matter what I did. now, I get around 15-17. I have some upgrades, but I am also having a lot of issues with the motor right now.

[AKMark]

Tried a different fueling place. Glad I did.

Running short trips (14-18 miles at a time usually) I'm averaging 18-20 with summer weight fuel and a little bit of 2-cycle oil to give me some lubrication.

I haven't had a long road trip since using this stuff, and my bad luck I will be back to winter fuel before long. Summer doesn't last long here.

I found two of the other stations I used to fill at run winter fuel all year round. Jerks.

[Rhynno]

I have had my 2005 GMC 2500HD Duramax for over a year now, and it gets horrible fuel mileage. It is lifted with 35" tires, has an aftermarket air intake system, Edge Attitude chip, and aftermarket exhaust (not sure on the gears, assuming stock). I get between 10.5 and 11.5 MPG. At first, I thought it was the chip because it was set to Stage 3 and had tons of power, so I changed it to Stage 1, the economy setting. I only gained .5 MPG, so I changed it back to Stage 3 to get the 70hp and the 120 Ft. lbs. of torque. I also have a 2000 Ford Excursion 7.3 Powerstroke which I have owned for 14 years. It is much heavier than my Duramax, especially when the 44-gallon fuel tank is full. It has a 6-inch lift, is running 37" BFG KM2 M/T tires, and the gears are stock. For the life of the Excursion, I have averaged 17.3 MPG around town and I have even been able to achieve 20.4 on the highway, loaded down with camping gear and people. The big difference I see between these vehicles is the Excursion has hubs and the Sierra doesn't. I haven't had a lot of time to work on the Sierra, so I am sure I will be able to tweak it some once I can spend a little time and money on it, but I was hoping it would at least deliver 15 MPG around town. I hope to get one of the hub conversion kits from the Ram Man this year and get that installed to see what difference that makes, but at this point, I have just done routine maintenance. I will also give it a tuneup when time allows. Love the truck though, drives awesome, very comfortable and get amenities!

[wmholden]

In 2005 I averaged 21.7 mpg on a trip from Texas to Savannah @ 67.5mph. Last week I averaged 18.5 over an 800 mile trip, half of which include about 1200 lbs of hickory in the bed and 70-75mph. So I have no complaints. I love my LLY. And since I now live in town(again)my city mileage is 13.5 to 13.9 mpg. We are looking at the DT400 performance package now. We are approaching 160K and are ready for mods.
DT400 components for under $800 total look like a nice foundation for performance- now and future. I hope to find reviews on the DT400 kits