Expected fuel mileage 2wd crew cab dually?

[cowboy4123]

Now that I cleared up my false rpm reading. I have a 2wd auto crew cab dually... with 117k on the odo and previous owner told me "long block was replaced @ 83k".... I run at 60mph between 2200-2300rpms (maybe a 4.10?) What kind of fuel mileage SHOULD I be getting with this truck?

I've currently clocked the best at 13.73mpg unloaded and worst 9.62 towing.

I've had the truck now for only 2 or 3 thousand miles....

[AKMark]

A friend of mine with a 99 Suburban with 4.10 gears gets no better than 14 as well. I think that gear is too deep unless you tow most of the time.

[More Power]

I've currently clocked the best at 13.73mpg unloaded and worst 9.62 towing.


Long-term averages that account for several tanks of fuel produce the most accurate results. It's also helpful to know what type of driving you do. Commuting in traffic, stop-n-go town driving, short distance driving, etc will all produce lower mpg than a constant speed on the interstate for all or most of a tank of fuel. There could be 3 mpg difference between short distance mpg and Interstate mpg.

A typical unloaded 6.5TD 3500 dually with 4.10's produces 15 mpg (some have reported up to 17) while on the interstate at 65-mph. Assuming your speedo and tach are accurate, and you are running stock diameter tires, you should be seeing 2250 rpm at 65-mph.

Jim

[DaveNY]

I get on average combined on a typical usage about 13-14, on hwy 600 mi trip to nc I usually get about 17-18 holding it around 65 mph.
Dave

[cowboy4123]

I just got back from this weekends jobs towing in mostly mountainous hard pullin terrain and only got 250 miles out of my 34 gallon tank. Yes I do towing most of the time (thats the point of this truck). But 7-8 mpg is disgusting! My old cummins never ever sucked more than 10mpg even when the trans broke, starting in second gear. My 24 foot box truck even gets better mileage loaded!

Ok enough yapping, any body think changing my gearing from 4.10 to like a 3.5 (whatever the next step is there) would improve my fuel mileage while towing? And yes I'm running stock tires 225/75/16's and also towing more than 6k pounds on a regular basis......

Also what would that involve electronically on a 94? New eprom?

[AKMark]

I'd step up to 245/75 tires, or see if you can pick up another 14FF rear with 3.73's and see if you like it.

While towing that does seem like it's using a bit much. Lots of factors to consider there. Do you tow in OD or 3?

[cowboy4123]

I tow in both. Bein theres a lot of hills here, If i'm on flats or degrades I'll keep in od, soon as i feel it start to lug I kick it back down...


Whats a 14FF?

I noticed SSdiesel supply has "fuel-miser" e-prom and injectors, any experience with either of these products? I figured if they actually save fuel that would make up cost/time for a gear swap, and assuming I might need injectors anyway................:confused:

[6.5 Detroit Diesel]

14FF=GM Corporate Full Floating 10.5" Axle. Very easy to setup the gears on and fairly common and cheap to get. Being a diesel, you should have the Gov-Lok setup, so if you want to keep the extra traction, you need to find just the ring gear and the pinion gear from a 3.73 set.

I ran my truck which is 4X4 with 4.10's through the Rockies yesterday towing a 14" trailer and got just over 15 mpg. Nothing on, going through the mountains between 16-17 mpg.
I would step up your tire size before you go changing gears though. If you tow a lot, than the 4.10's come in handy.

[Busted]

I drive a 1982 CC dually 4x4 with a somewhat modified driveline (see sig :D) and get about 14MPG US while towing around 5-6000 pounds. Haven't had a chance to work out mileage running empty yet . . .

BTW, Ben, I'm guessing your mileage numbers are Canadian gallons, multiply by 0.83 to get US numbers, and changing tire size has the same effect as changing ratios, just not as permanent . .

[ttpost]

225 75 16 is what a think your running (29.28 inches in diam) 245 75's may rub together on a dually (30.46 in) i would go to 215 85 16's (3o.38 in) or even better 235 85 16 (31.72 in) as long as you have clearance and just change your rears since you are 2wd. it is alot cheaper than changing a rear end, especially if you go used. just make sure you have clearance between you duals, if you could fit (more and likely with spacers) 255 85 16's yould would be at 34.063 in and that would be a significant change (alot cheaper than gears). if you find where you want to be on tire size you need to recalibrate your vssb to correct your speedometer for correct readings to your computer and your spedo, it is really easy to do, you can find the info by googling chevy vssb. hope this helps rob

[6.5 Detroit Diesel]

Nope, using American gallons. (3.78L/1gal)