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Gas Mileage for 2500HD 8.1L 6Spd Auto


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#1 mark97213

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Posted 16 August 2006 - 10:12 PM

2006 Silverado Ext Cab Short Bed 2500HD 8.1L Vortec 6spd Allison

I realize that to even ask a question about "Gas Mileage" for this type of truck is pretty immaterial as to it's purpose. However, I am still curious as to what I should really expect to obtain when it comes to mpg.

Currently, in town driving, I am averaging 5.6 mpg. When I take this hunting in the fall and tow a trailer, I can probably expect a little improvement since a lot of it would be Hwy miles but I would expect an little better rating. Seems beyond inefficient, it seems VERY inefficient and not indicative of the technology. I imagine this is why GM won't offer this motor in 2007 or so I'm told.

This Mileage does indeed suck, literally, but I wouldn't trade it for a Duramax that obtains 20 mpg . . . I love the 8.1 and what it can do. However, since there was no mpg rating on the sticker, I have nothing to base my actaul mpg on as to whether or not it should be better. Does 5.6 mpg sound right? Can anyone else with the similar Truck give me a comparrison?

Edited by mark97213, 16 August 2006 - 10:13 PM.

Democracy is, two wolves and a lamb voting on what to have for lunch. Liberty is, a well-armed lamb contesting the vote! Make yourselves sheep and the wolves will eat you."

#2 k3500CC8.1

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Posted 17 August 2006 - 07:41 AM

5.6mpg is way to low. I used to get 4-6mpg with a 1996 K3500 ext. cab with the Vortec 454 pulling a 15,000lbs trailer across the Rockies, with a headwind.

My current new truck is a K3500 CrewCab dually with the 8.1Liter Allison 6speed. It's not a everday driver and I've only put a litttle over a 1K miles on it since April, so this is very early data and really just a range right now. I'm getting between 10-11.5mpg in town and 10.5-13mpg on the highway. That's hand caculated but the DIC is usually within a 0.5mpg. The highway mileage is totally dependant on the rpm you cruise out. I have not towed with this truck yet so no data to report.

I did own a 2001 K2500HD ext. cab shortbed with the 8.1Liter 6speed manual. That was the best truck combo I ever owned. Put over 100K on it before I sold it. In town I would get between 10-12 mpg and on the highway I could get as high as 15.5mpg on long interstate trips. At 80mph, that truck would get a constant 12.5-13mpg. Actually at 80mph and up, the truck got better mileage than the 2003 K3500 ext cab dually duramax 6 speed manual I owned. I towed a 40ft gooseneck flatbed with the truck a little over 10K miles during the time I owned it and the mileage ranged 9.5mpg at a 10,000lbs trailer weight to 7.5 at a 18,000lbs trailer weight. The 2003 Duramax only averaged 1.5 to 3mpg better than the 2001 8.1L pulling the same trailer and weight.

I guess I'm the only guy in the world that sold a Duramax and went back and ordered a 8.1Liter. For all the complexity and price of the Duramax, I just wasn't impressed with the performance. And I kinda like the idea of being able to work on my truck's engine with confidence. Call me Crazy, but I love the old big block. No Diesel Envy Here!!! Really though, the 2003 Duramax was a great truck that never left me wanting more and never left me on the side of the road.

Hope this helps...

Edited by k3500CC8.1, 17 August 2006 - 07:43 AM.


#3 dewfpo

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Posted 17 August 2006 - 01:48 PM

Something's wrong at 5.6 city mpg. Either something is busted, you idle the engine an awful lot or your flooring it all the time. The lowest I've ever gotten with mine (all city, no towing) is 9.03 mpg.

If it's a new truck with just a few miles and you going by the DIC. I"d reset it. When I picked up my truck, it had 7 miles on it and the DIC said 3 HOURS of run time!! :banghead: I think the fellow that detailed it left the engine running the entire time (December 17th) and the radio playing.

My best (non-towing) has been a right at 14 mpg at 65 mph. And that's with a 5 speed.

DEWFPO
2005 Silverado 2500HD, CC SB, 4x4, 8.1L/Allison, 4.10's, Locker, Dual Batteries, 145 Amp alt., Bilsteins
Retrax Rolling Tonneau, Putco SS/Chrome Side Rails, Bushwacker Bed Rail Protectors,Husky Floor Liners

#4 mark97213

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Posted 20 August 2006 - 02:00 PM

Something's wrong at 5.6 city mpg.  Either something is busted, you idle the engine an awful lot or your flooring it all the time.  The lowest I've ever gotten with mine (all city, no towing) is 9.03 mpg.

If it's a new truck with just a few miles and you going by the DIC. I"d reset it.  When I picked up my truck, it had 7 miles on it and the DIC said 3 HOURS of run time!! :cheers:  I think the fellow that detailed it left the engine running the entire time (December 17th) and the radio playing.

My best (non-towing) has been a right at 14 mpg at 65 mph. And that's with a 5 speed.

DEWFPO

<{POST_SNAPBACK}>


Yes, I am thinking something is wrong. It's a brand new truck that even with the big block... it shouldn't be getting this low. I have no long idle times nor am I floorin' it . . . just typical city driving.

I've reset it a few times and still comes up the same. It runs well but something sure seems wrong with thhat mileage. I'm takin it to the dealer on Monday to have some painted fender flares put on so I'll ask them to check it out. What could it be that they should check? I don't think I have a sticky egr valve or anything like that but??? Any ideas what it could possible be??
Democracy is, two wolves and a lamb voting on what to have for lunch. Liberty is, a well-armed lamb contesting the vote! Make yourselves sheep and the wolves will eat you."

#5 Haulin' 8.1

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Posted 20 August 2006 - 03:31 PM

Mark as a professional technition I'll tell you it could be a bunch of different things. Just tell them the problem and hopefully they're able to find it quickly.

Vernon
2001 Siverado HD 2500 SBCC in Black
GM Vortec 8100, Allison, 3.73, 4X4
Mods: Goodmark SS cowl hood, Ranch Hand bumpers, black toolbox, custom bed cover, full tint, Volant with home made ram air, BBK 80mm TB, Granetelli MAF, Marine Injectors, Hypertech, Champion RS12YC plugs, Magnaflow 3" dual in X-path dual out muffler and tail pipes, Fuzion XTi 265's, Velvet Rides, Pioneer 10" subs, amps, you know the usual stuff.
Coming soon: 4.56 gears, Autorotor supercharger by Whipple with Duramax intercooler, and GM HP3 cylinder heads.
If you've modded your 8.1's timing and run hard try Champion RS12YC plugs gapped at 0.055". Less knock, more power. Yes you have to change them more often (25K), but this is a performance mod. Besides they're cheap and easy to do.

Yea though I drive the the valley of the shadow of Diesel,
I will fear no turbo;
For your horsepower art with me;
Your bore and stroke, they comfort me.