El Slurpo (Vertec 8.1 liter)

[Montana_1410]

I've recently upgraded my truck to a used 02 Chevy 3500 8.1 L, Crew Cab Duelly with 16,00 miles on it. I upgraded from a 2000, 3/4 ton GMC with a 350 engine which pulled my old trailer with marginal performance (and eight miles / gallon pulling the trailer) With the purchase of my Montana 2005 2980 RL I figured better performance with the new truck. I got better performance, love the truck--Allison transmission and all-- but my fuel mileage is dismal.

Pulling my 26 foot pull trailer, 8 mpg. Empty, City or Highway, not pulling anything, 8 mpg. Pulling my new 2980RL, as low as 6.7! I hear from dealers that this truck SHOULD get 12-15 mpg empty on the freeway and around 10 mpg pulling my trailer, their mechanics just smile at those claims. I'm still under warranty so aftermarket fixes haven't been considered. I'm a commercial driver and know how to drive for better mileage so driving technique isn't my problem.

Several questions: Is this mileage to be expected from this truck? Do you with similar trucks get any better mileage? If so, how? Is there anything I can do, short of diesel, to significently improve these figures?

Thanks for you time in responding to my problem.


Myron

[tweir]

Hi Myron,
I have an '02 2500HD with the 8.1. I too, ran into the mileage problem. What rear end do you have? That can have something to do with it. I learned, when at all possible, to keep my rpm's under 2k. Its impossible when pulling hills, but I've gotten as much as 9+ mpg while pulling a 3685FL. Empty, I hover around that 11.5 to as high as 14 mpg empty. You may want to see if GM has any "flash upgrades" for yur computer. If I'm not mistaken, they will do this under warranty. The only time I use Tow/Haul mode is when I'm driving in hilly terrain. I don't know if this helps or not.

[sreigle]

Myron, there may be some room for improvement in your mileage but I'd be surprised if it gets much better. We used to have a '99 F350 with the V10. That's a 6.8L engine as opposed to your 8.1L V8. Towing our 3295RK we averaged 8.2mpg overall. Solo in town we got 11, sometimes 10. On the highway at 65 to 75mph we averaged 11 to 14 with 12-13 being most prevalent. I know yours is not the Ford but you did ask about similar trucks so I thought I'd toss in it's not just GM, it's big gas engines in general. We had the 3.73 rear axle and automatic transmission towing 12,500 lbs when weekending and 13,980 when fulltiming.

[lightningjack11]

In comparison to an old diesel, on my most recent trip of 4800 miles My avg milage for those miles was 12.5. From Kansas to PA I average 13.5. I know that does not help you but if your looking for power and economy, you have to go with a diesel. These old 7.3's are now turning 400000 without overhaul. That is when the speedometer resets. Avg price a gallon was 1.65.

If you can find a bargain on one I suggest you pick one up.

[8.1al]

I have a 2001 with 8.1 and 4:10 rear. City/Hway 12-13 empty,highway14,towing our 3575 RL 8mpg overall some days better, some worse.

[Northstar]

I suggest you purchase a diesel for a number of reasons: better mileage, more power, cheaper fuel, longer engine life, etc. Lots of good reasons to buy a diesel. Happy rving....

[DrivesBGM]

Myron,

I am getting around the same as you. I have the same setup as you. (I assume you have a ax4 with a 4:10 rear.)

The worst I've seen towing is 6.5 mpg. The best I've seen empty was 12.5 mpg.

I just think of my 8.lL as being GAS COOLED! And it is quiet and pulls very well. My Chevy 3500 has done everything I've asked of her these past 28 months of ownership!

Craig

[Montana_89]

Myron,

Welcome to the "8.1 club!" As the signature shows, my dually gets about the same as the rest! I have run two long (1000 miles and 1500 miles) trips in the past year. Empty the truck gets 11-12 mpg. Pulling my 36-footer it gets 6.8 mpg to 8 mpg. I tow at about 65-70 mph and I know that doesn't help. Unfortunately I am NOT retired and I have to make time on the road. I will be traveling to Florida in August (3500 miles) and I can give you a follow-up. I pull in "tow-haul" mode all the time AND in overdrive. I still haven't determined if I should "lock out overdrive" since most of the time is "stays in" while towing. I haven't determined if running 3000 rpms (under no strain) will equal running at 2300 rpms in overdrive. As said by other "8.1" owners, the truck pulls without any problem BUT IT DOES USE FUEL!

[BigBlue]

Myron
I have a Chevy C4500 with the 8.1 and Allison tranny. I get 7 mpg whether I'm pulling anything or not. I have the 5.13 rear end so my mileage is lower than a 4.1 is. I've checked on the GM Forum and several of the experts there said my 7 mpg is pretty good. As others said, big engines use fuel.

[Bob Pasternak]

Hey, we had that 8.1 in a 27' class "A". Got it all the way up to 10 MPG one time going down Monteagle in TN with a tail wind. I was gonna have my girl friend take a picture of it but it didn't stay long enough!!!