View Full Version : What mileage are you guys getting with your GM 8100?

09-16-2003, 11:37 PM
I've got a 2003 3500 chassis cab with a flatbed. It has 4.11 rearend and Allison.

I'm getting an average of 5.5 mpg with a low of 5.3 unloaded last week. I've never gotten better than 6.0 mpg.

Chevrolet is saying nothing is wrong, which I believe is nuts. The computer "tells" them there is nothing wrong. I think the service guys believe in their hearts that something is not right, but Chevrolet wont authorize them to dig deeper without the computer saying something is wrong.

I'm frustrated with the situation and wondered if anyone else is experiencing this and possibly has insight into this issue. The guys around here are getting 9-12 with highs around 14 and the worst I've heard of is 7. The 7 was towing in the winter with lots of warm up time after starting.

Gravel Rat
09-17-2003, 01:58 PM
Hey you own a big block gas what do you expect my old fuel injected 460 in my F-Superduty got 8mpg tops averaged 4-6 if I was hauling heavy loads she would burn a tank of fuel in half a day. The old F-Superduty with a dump weighed in at 8200lbs I used to carry upto 8000lbs of gravel on her grossing 16,000lbs .

If you want fuel economy get a diesel I went to a 7.3 N/A with a M/T truck I see 12mpg with a loaded truck I see 8mpg its a bit slower on the road but atleast it doesn't require me to fill it up twice a day.

For me to drive it around a average day costs me 10 bucks in fuel the gasser was 20 bucks per day in fuel I just couldn't hack the fuel consumption of the 460.

09-17-2003, 04:31 PM
Since I bought a bigger trailer,and added a turf tiger to it my 460 has been getting 7mpg.I believe I'm going to try Izuzu NPR diesel next.

09-17-2003, 07:55 PM
I realize the 8100 is going to be a gas hog. I've had and currently had diesel trucks and understand they get better mileage, but like I said earlier, I'm trying to figure out the discrepancy between guys I know with the 8100 getting 9-12 and my exact same truck getting 5-6. I can't figure out why I'm getting half what they are getting. I realize it's a big block, I knew it would be bad, but this is really, really bad. I'd be cool with the mileage others with this engine are getting around here.


Gravel Rat
09-17-2003, 08:27 PM
Are you sure the other guys are telling you the truth because its hard to beleive that a 8.1 l engine is going to get what you said they are getting.

Fuel economy depends on so many different variables like how the truck is driven where its driven how heavy the truck is and so on and so on.

I wouldn't be surprised if you get any more than 10 US mpg especially in a 1 ton cab and chassis with a flatdeck on it.

09-17-2003, 10:55 PM
JLC - 4:11 gears will eat up mileage. What gears are in your buddy's truck?

09-17-2003, 11:44 PM
I have a Duramax, but my friends that have the 8.1 are getting 9-11 mpg. 5 mpg sounds way too low.

09-18-2003, 03:01 AM
One specific friend has a 2002 Chev. 8.1 liter allison auto and 4.11 gears. It is used on a farm heavily. He averages 10-12. Had a best of 13. something all highway miles. Worst of just under 8 pulling a silage wagon against a strong headwind back from a farm auction. His truck is a single rear wheel crewcab. Not sure if it was a 2500 or 3500, but the drivetrain is the same.

09-20-2003, 03:17 AM
I used to sell chevy trucks before I quit to do lawns. I don't think I ever really met anyone that bought a 8.1 that got over 7mpg. The 6.6 gets 18mpg and the 6.0 usually got somewhere between 12-14 depending.
I pull a 14foot landscape trailer with my 5.3 short bed and get about 16.5-17mpg. Plenty of power to boot.

09-22-2003, 01:59 PM
I just traded a 01 GMC 2500hd with the 8100, allison, 4:10. Loaded with my 20' enclosed doing nothing but city driving I usually got 8-9. Highway empty I got about 11. It pulled great too. Before this truck I had a Crewcab Chevy dually with the 454 and my mileage was much worse and not nearly as much power. I had it back at the dealer several times and they would just tell me that it is a big truck and its not going to get good mileage or have much power. Just their typical answer I guess!