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2000 C3500 C&C poor fuel economy: suggestions?

GM Guy

GM Guy

Manual Trans. 2WD Enthusiast
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Location
NW Kansas and SC Idaho
Dad took the new truck on its maiden voyage, and is not too impressed with the fuel economy. 2000 C3500 Cab and Chassis DRW 5.7L Vortec 4L80E auto, 2wd. (pretty sure it has 4.10s)

Before he left, we changed oil and put Wal-Mart (I know, it will not be in there long...don't worry) 10w30 synthetic in, and the tranny and diff just got topped off, Dexron III in tranny of course. It got 13mpg empty, with a slight tailwind as well. speed was 65mph.

Loaded, it did bad, ( 9mpg) but it was to be expected, as the piece of farm equipment was fairly heavy, and it caused alot of wind drag as well.

Is this normal, or do the upstream O2 sensors need changing? I've been told that they will go bad, and will sometimes not throw a code.

The 98, identically equipped, except 5spd manual, will get 10-11 pulling a decent sized trailer loaded down with stuff. recent trip gave us that mpg with a 6-row 30 inch cornhead on the trailer. Should it be getting better mpg as well?

The 98 has 208,xxx miles, and the 2000 has 61,xxx miles.

Any help appreciated, thanks!
 
That sounds normal, unfortunately. I've said this someplace else before, but a friend of mine had a 2000 GMC 2500 CC 2WD with the Vortec 5.7, 4L80E and 4.10's... it got ~10 and 11 mpg no matter what. It was a big, heavy truck that got the job done, but the engine is a touch anemic for such a big vehicle.
 
Sounds about right from what I remember from past trucks..
 
Golddigger said:
My 1999 1500 suburban only gets that! I feel your pain.
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Thanks! ):h

woodchuck2, I have a counteridea, sell the 2000 truck w/ 60K miles to fund the possible cummins transplant into the 92 if/when the 6.5L dies. Wiring will be way more simple.:thumbsup:

Dad would much rather dump a cummins into one of his project IHC pickups. He still likes his International pickups better than his GMC pickups. Many arguements over that subject.....:D
 
Does anyone think that upstream oxygen sensors may help? I do not think the 00 will need them at 61K, but the 98 may at 208K.
 
13 is pretty good for that truck, I wouldn't spend the money on the O2 sensors. Last place I worked had a 92 C3500 SRW CCLB truck. 9mpg was about as good as it ever got. The 350 just doesn't have the snot to handle the weight. It will do it for a long time and not die (that one finally blew the original head gasket at ~315,000 miles), but it's working it's tail off, so they get poor milage.
 
There is a rolled '99 quad cab cummins for $4,500 . 198K. My only other thought for my burb is efi live cause then I can use it on my truck to.
 
Yeah, the 13 empty was not great, but with a 2-3K blade plow (aka Alfalfa crowner, sweep machine) it was a 3 section, and w/ wings folded up, it was close to 11 feet tall on the truck. all the way home, dad had to deal w/ a 15-30 mph sidewind. so really, the 9mpg loaded was actually not half bad. I thought it would get around 6!

Gas is going up here too......crap.
 
I think you're doing well for mileage. We have an '04 2500hd 6.0 work truck. It has racks/side boxes and we towed a 16' enclosed trailer to Wyoming and back from Michigan. We saw one tank get 5.9 mpg. We had also used 87 with Ethanol....so we figured out it killed our power and mileage. This was also going into the wind but the trailer maybe was 5k loaded. We ran Premium the rest of the trip. The best we got on the way home (our trailer now lighter from use of materials) was 8.9 mpg but that was the only tank that did that well. The others were about 7-7.5 mpg. Our trailer was also lighter now because we used some materials. We were also going 82 mph in a 75 and 72 mph in a 65. ):h BUT, we yielded the best mileage when we were going 82ish in Wyoming up and down hills/mountains. :nopity:

Needles to say, my dad was not happy. He wants a Duramax but we can't afford new work trucks right now.
 
My Tahoe w/ the 5.7 never got over 16, with me DD'ing it 20 miles each way. Worst tank was 9, when we were towing stuff with it instead of the D-max, because I believe the D-max was getting fixed.
 
That mileage is just right. Dont expect more. Its a big truck with little motor unfortunately so that bout it on mpg. Hell I dont get those numbers with mine. Empty highway @ 80-90 mph I get bout 12 on a very good day. Was better at 65-72 mph but I cant go that slow. Loaded I see 5,6,7 in city. Usually 7 mpg is the norm in city unloaded. I get bout 150 miles to a tank in town.
 
That is a very small motor tryin it's hardest to move alot of weight it is doin decent in the mileage department, I have never had one get more than 13 myself. Could be worse man, the old 454 gets 9mpg period at the most the worst I have got was 2 mpg with the cat 426

I would say you are fine just my .02
 
make it breathe better, true duel exhaust, heads, cam. give it a tune up if needed too. you can get 1-2 mpg more out of it with a little work.
 
jcool said:
make it breathe better, true duel exhaust, heads, cam. give it a tune up if needed too. you can get 1-2 mpg more out of it with a little work.
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That's easily over a grand to get it up to what...11mpg?

Run it like it is, a small motored heavy truck.
 
JeffsJeep04 said:
That's easily over a grand to get it up to what...11mpg?

Run it like it is, a small motored heavy truck.
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depends on how far he wants to go, yeah that could cost alot but also bring some more power to boot. even if he only gains 1mpg and 40hp/40ftlb tq. it would pay for itself if he kept the truck a while and drove it regularly. i had quite a bit of money tied up in my 03 5.3 silverado with most of those parts and then some and went from 17mpg highway to 21mpg highway, truck had quite a bit more power too. the real question is if he likes the truck enough to keep it? if so why not modify it a little for better power/economy?
 
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