Terrible mileage

[steampunk1375]

So I've had my OBS CCSB for a little over a week now, and it's getting terrible milage. And I mean terrible. It's a K2500 5.7L/4L80E with 4.10's but I should get more than 180 miles to a full tank of gas.

The truck starts very easily, has no codes stored and the engine light is not on. It idles smooth, the air filter looks ok and the coolant temperature sensor is within spec. Any ideas where else I might start? I have not had a chance to check plugs/wires/cap/rotor but they look fairly new from the outside. When the weather clears up I'll check all of that. I'd suspect the MAF sensor but I'd doesn't have any of the normal symptoms, aside from the aweful milage this truck runs beautifully.

Any help would be great. Thanks.

 

[woody31]

check the air pressure, and alignment, make sure your brakes are not dragging,,do a full tune up with good quality parts,,replace the o2 sensor,,clean the throttle body,,what about the exhaust,,does it have a cat on it,,,is it plugged up??? all this can add up to horrible gas mileage ,,ck for stored codes,,just cause the light is not on does not mean there is no codes...check and do all this,,report back plz,,thanks

 

[steampunk1375]

Yeah there's no stored codes. I said that already. Tires are good and like I already said weather permitting I will check everything else. We've been swinging to -15 and it just snowed another 4 inches last night. So does anybody have any experience with milage this bad being a component related failure?

 

[thz71]

What ru getting for mpg?

 

[great white]

Well, assuming the 35 gallon tank and 180 miles you're getting around 6 miles per gallon.

That is from full to dead empty. I would say you're doing a little better than that of you log your fuel.

I would say you need to log a couple tanks to find fuel burned for an actual mpg figure.

Now, if you're around 8-10 mpg, thats not very far out of line for a 350 pushing through a 4L80e to 4.10 gears on a heavy ccsb truck in the dead of winter. Even more so if you're predominantly short trips or in traffic. Warmup time in winter also kicks the crap out of mpg. My diesel is equipped like your truck and it dips to 11 mpg in the dead of winter. Pulls somewhere between 16-18 summer on the highway.

Your truck is only about a 15 mpg truck on the highway in the summer on a good day.

Welcome to owning a big truck with deep gears.....

 

[thz71]

Im guessing your not running your tank very low for one i think of you actually figured you mileage you would be right on par for those trucks

 

[steampunk1375]

Well I'm Canadian, so I'm doing some conversion work for you guys south of the boarder. Bear with me.

62.393L of fuel for 269.5km
Works out to 16.48 US gal for 167.46 miles or I believe 10.39 mpg, that's with short warm ups (5 min) and I drive 90% highway miles to work.

I have never seen one of these this bad. I've worked on 5.7 duallies that got 16mpg regularly. I guess the question might become how much of a benefit would I see by switching to a 3.73 or 3.42 gear set. I have a matched pair of diffs out of a 94 that I think are 3.73's. I'll check them out when the snow recedes a little more.

 

[thz71]

My 2000 454 with 3.73 got around 8 mpg

 

[great white]

Well I'm Canadian, so I'm doing some conversion work for you guys south of the boarder. Bear with me.

62.393L of fuel for 269.5km
Works out to 16.48 US gal for 167.46 miles or I believe 10.39 mpg, that's with short warm ups (5 min) and I drive 90% highway miles to work.

I have never seen one of these this bad. I've worked on 5.7 duallies that got 16mpg regularly. I guess the question might become how much of a benefit would I see by switching to a 3.73 or 3.42 gear set. I have a matched pair of diffs out of a 94 that I think are 3.73's. I'll check them out when the snow recedes a little more.

I'm Canadian too my brother.



10.39 mpg is within what can be expected for your truck.

My diesel has been getting around 12-13 mpg with this extended cold snap we're all bloody tired of dealing with.

Mine is a 1998 K2500, eclb, 6.5 TD, 4L80E, 4.10. I need the 4.10 gears as my trailer scales in right around 8500-9000 lbs.

You can realize a bit more mpg with 3.73 a and give up some "grunt" if you don't tow.

 

[steampunk1375]

I don't need it for towing really at all. I'll haul a few ATV's (3-4, 700lbs average each) a few times a year, and twice a year I'll probably put a camper on and drive a few hours to the lake for some camping. That's it. I'm not hauling a fifth wheel, car trailer or horses. I don't need the 4.10's as much as I need the milage.

Any idea what sort of mpg gains a person would see switching from 4.10's to 3.73's?