2004.5+ LLY Duramax Fuel Economy Poll

[belcll]

Originally posted by MPH:
I too have been a little dissapointed in the lly's mileage. driving home from the dealer it averaged 18.4, which I was impressed with, but it has never been that high since. Pulling a little two place snowmobile trailer, i was only seeing about 11 mpg. I put 305's on it right when i got it home. could this have affected it that much? It didn't seem to drop the LB7 that far.

[belcll]

oops, did a false post. I added 285/75 tires and notice my mileage fall almost immediatly by about 1-2 mpg.

Originally posted by MPH:
I too have been a little dissapointed in the lly's mileage. driving home from the dealer it averaged 18.4, which I was impressed with, but it has never been that high since. Pulling a little two place snowmobile trailer, i was only seeing about 11 mpg. I put 305's on it right when i got it home. could this have affected it that much? It didn't seem to drop the LB7 that far.

[Freeman777]

I participated in this survey (15 - 16 mpg city and 17 - 18 mpg hwy) a day or so after the poll was posted. I've been back several times since and noticed that the majority of the LLY owners fall into this category. I've been in the high 18's on several occasions, but didn't feel justified in voting in the 18 - 19 mpg class. Yesterday, on hwy #95 (just North of Las Vegas, NV) I ran a test under ideal conditions of road, wind, terrain, etc. and marked 20 miles at 70mph on the cruise control. The result was: 23.2 mpg according to my digital information center. My rig is a 2004.5 GMC C3500 CC, SLT, LB, 4WD D/A (LLY). After 6 mo. of use I now have 15K and the only thing I've been doing differently is using a fuel additive: Power Service -8 oz. per 25 gal. (states on the container: "absolutely no alcohol") Although this truck is running GREAT! I wasn't happy pulling a 36', 14+K, 5er over Baker grade (I-15 bet. Stateline, NV and Baker, CA) in 2nd gear, at 35mph at 3,500 rpm and both temp. gauges too close to hot for my comfort. Trips like that to San Diego resulted in 10mpg. Since my last trip, I've been anxious about the new Bank's set-up (in R&D for quite some time) for my LLY and got the GOOD NEWS call today: A six stage system (air filter, six-gun controller, exhaust system, boost and pyrometer gauges) that will selectively and progressively boost my engine/trans 128 HP and 345 fp torque. Stage #1 is the stock setting and every stage thereafter = a 20% boost. By going with the unique design of the Banks set-up, I think my engine/trans plus my 100,000 mi. after-market warranty will be better protected.

[eagle in flight]

My LLY has been getting about 18 mpg all by itself. When I tow a fifth wheel (weight around 14,000 pounds) and travel at 60 mph, I get around 11.5 mpg. Mileage is at 15,000.

[fishhead1076]

At first very disapointed with the lly and fuel milage, my average was around 12 no matter what towing or mt. After 12K and first fuel filter change my milage changed drastically, went from avg. of 12 to 17 in the city and 18+ on the highway. Didnt really buy into the break in better fuel milage bit, but I must say I was suprised.

My 2 cents...

[tanker]

Well just picked mine up last Monday night, did some round town back and forth to work running, then stretched its legs down to Virginia this weekend and the computer says 16.6mpg, not so bad running 70mph, Opps not supposed to go over 55mph in the first 500 miles, but ran well, didn't do any major acceleration's just cruised along with traffic. Should improve as it breaks in. First 100+ miles in stop and go driving, some high idle warm-ups. Will wait and see. Can't wait to hitch up and go.

[jogger]

Did a short 150 mile round trip consisting of mostly freeway and rural driving and averaged 21MPG for that trip. In the city I average about 18.

[guerrero]

First 430 miles coming back from the dealer in Kellogg Idaho with outside temps hovering in the high 20's and several inches of snow on the ground through one of the mountain passes requiring prudent use of 4WD on I-90, averaged 20.5 mpg. Very happy with these results and expect additional improvements when I get the truck back to PH Hi and the warmer climates.
2005 PDN extended cab

[mjammer]

I am seeing 17.1 for mixed driving on my new truck, 2500HD D/A 4WD CC LB (just picked it up Friday) in the first 200 miles. That is better than I ever saw on my old gas 2500 extended.

[Mile Hi Guy]

Well I have roughly 17,000 miles on her now I got 16.0 twice (I do check every tank manually) but usually average low 15's empty driving mostly a 80% Hwy commute. Traded my brother one week (10 days actually) and got 17.2 doing the same routine in a 2001 AWD Denali

Truck runs ok but not nearly as strong as by Brother-in-laws 05 CCSB Ford 6.0

Had the truck in twice and they say everyting is ok in the motor department. The only thing they cannot seem to fix is the Drivers seat will not keep it's memory and a whistle on the passenger side door. Would that qualify for a lemon?

[Shire Ben]

I have a 2004.5 LLY which I purchased in Mar 04 with 24K and I consistently get 19 mpg hwy. No modifications or upgrades. LOF every 3K and FF every 15K. Had similar experience with 2001 LLY which 85K, same maintenance, no injector problems..Thanx

[pepper]

I have gotten 22 mpg on a tank full but I had to keep my foot out off the accelerator, 62 mph or slower and no repeat no hard acceleration, that is no fun so usually hit a few times per tank and get 18-19 - towing the boat i get 13-14 it is a wide flats boat with center console which is more of a wind trap than a weight issue, heck i only got 12-13 highway with my old gas van, wish they had a van with this eng/tran setup. I'd have one tomorrow, yes w/4wd!

[Dewey Faircloth]

Get 18 to 19 driving empty 13.2 pulling travel trailer staying about 65.
Leaving Saturday going to Camp Lejuene pulling trailer and will see if it does better now has over 12,000 miles on it,fresh filters and gravy.

[Jerry D]

Today's 50 mile journey of back roads and HW had me average 22 MPG according the DIC. I'm wondering if when I filled up a couple of days ago I got my first tank of Non winter fuel because this is better than I've been getting recently.

[Curt B.]

Just wondered how fast most of you drive, that are seding 18+ mpg? I drive 75-80 on interstate most trips, and I have yet to get over 17. Today with 30 mph tailwind, DIC was showing 20-21. I never get that on a normal trip.

[KCDuramaxTurbo]

300 miles so far 05 lly, first tank, home from dealer 20.0, now 18.2. Really easy on the accelerator. Have a predator coming.

[Noal]

'05, 4x4 2500 HD Crew Cab. 3000 miles. Getting average or 16mgp town or highway. Had '02, same truck except 8.1 L gas. 60 % better milage. See the smile on my face.

[Shoe]

First post on the forum...

I'm sure hoping my the mileage on my 05 will improve as it breaks in. I'm milking it in order to achieve anything over 17. (still under a 1000 miles) The 03 was getting a steady 19 from the dealer and ended up with 21 at 65K. Sure seems the turbo kicks in at a lower RPM on the new one and it runs a little warmer than the 03 at higher speeds.

Great Forum!

[Wally1]

05 CC/4X4. About to fill up for my third tank.
So far 13.4 mpg all city driving.

[mjammer]

Wally, that is similar to what was seeing except a little lower as it was cold weather in February. Find an excuse to take a couple of log interstate trips to help break it it at more than just highway sppeds and see what it does on the interstate. My local driving mileage has seemed to pick up after some longer trips and the associated mileage. I am at 2500 miles now and see low 18's on interstate running ~68-69 MPH. My local mileage has picked up 1-2 mpg now.