I know that driving habits play a big part in mileage but I have never seen such a large spectrum for numbers.

I just completed another trip home to PA on leave and going up I got 19.2mpg driving 75 on interstae 95 for a few hours and between 65-75 most of the other highways and major roads.
On the way back I got right at 18.2 driving closer to 80 while on interstate 95.

I think my engine is a little noisy at times but I am more than happy with these numbers. It really makes me wonder what is up with some of these trucks. Habits vary but when folks are only getting 10-14mpg on the highways, something is wrong.

 

Had TSB 18-037-04 done about a month ago. It worked wonders. Did an 800 mile tow with a 3500 pound flatbed car trailer and averaged 17.2 mpg at 65mph. Mileage is now up to 17.4 on daily commute (not over 50 mph, a couple of traffic lights), 14.8 around town. Prior to the flash, best I could get was 14.3 on the daily commute, about 12 mph around town. Truck has 9500 miles on it.

 

I was averaging about 16.5. I am extremely pleased with the results

 

Poacher,
I have nearly the same rig as you and can only get about 15.5 empty on the road. I had the TSB 37-04 done and really believe my MPG may have gone down a bit or at least got no better. The OH went up about .7MPG but hand calc says it is not right. I wonder if there is some way I can tell if they really did the TSB? My truck is heavy also. I see numbers on here of around 7k. Mine full of fuel with about 400 pounds of passengers and a tool box worth about 200 and a few other items I suspect is about 200, I am at 8900 pounds. So, what can I say. I don't get the number others seem to get and wonder why. I drive very conservatively too; about 60 on the highway with an egg under my foot. This isn't a complaint exactly, but rather a qwest for knowledge

George

 

Thanks txhawg! I do think my friend has a problem with her truck... hopefully she'll get the TSB done.
Dave

 

The first tankful under 18-037-04 is gone. 510 miles. OHC said 17.6mpg. The fuel tank took 29.4 gal and that's all. Hand calculation says 17.3 mpg.

The last half of this tank was on really sloppy snow covered roads where the 33x12.50 Avons were pushing 4-6 inches of snow, uphill and down, in FWD, burning winter diesel #2.

Before the TSB, this truck averaged 14.5 to 15.0 on dry roads in 2wd.

Good enough for me.

 

GCROWELL, specs say a 3500 is around 800 pounds heavier than a 2500. Your number is about right.

7800
400 passengers
200 tool box
200 misc stuff
230 35 gal Diesel

8830

 

gcrowell

I used to drive it like there was an egg under the pedal. Gave that up. I don't beat on it. The only thing I've done is to make sure the tire pressure is at 65 lbs, and the tank is filled to the top of the neck every fill up. I let it glide as much as possible. Where the speed limit is 40, I bring it up to 45 mph to allow the converter to lock up, and slow it down to around 41mph and the converter stays locked. One other thing I noticed is it picks up 3 to 5 tenths on the overhead as the tank runs down below half, so the extra weight of the fuel must factor in.

 

I used to drive light throttle too. But hills took too long at a lower gear and the mileage suffered. Now I power up the hills and then feather the pedal on the level to get the lost tenths back.

Different than a gasser. This thing is pumping air all the time, and you control the fuel. Best situation is good road speed, low rpms and lightest possible throttle. Today I managed the whole darn mountain (12 miles) with a loss of 1/10th. Great truck.

 

One thing i wish i could test faster. i drive with the egg under the foot as well. also drive the truck as little as i can. Almost ready to click over 5600 miles. Hwy i can average 19-21 if i drive really nice at speeds no higher than 60. Ive had the relfash. get around 16 in town. Last oh 1/2 tank ive seen some friends i havent seen in a while and decided lets show the truck off. One big notice is that she didnt have the power that she had when i bought her. Use to be i could slam the fuel and turn the tires over ( get a lil not a ton but enough for impressions) She wouldnt do it again. But i drove her hard. Not beating on her exactly. but instead of slowly accelerating from the lights. I gave her fuel Kept u with the the traffic, stayed ahead of some.

Next tank showed 18.5 mix commute ( 60/40 city hwy) as apposed to my 17.1-17.4 since the flash. I dunno if its an cylinder clean up. I think the computers might learn driving styles as well. Learn how you drive and how best to fuel the engine maybe? Either way shes doing a lil better now. Just with i had some super heavy trailers to tote around

 

Economy... An interesting subject!

My 2500 is now at a little over 8000 miles. Never a tow behind this truck as we have two others ( '01 auto & '01 6 shooter) and I've been too lazy to hook up a brake controller.

Took a trip from our southern NY home to Reading, PA. Mixed conditions for driving from interstates to two-laners to an urban mess from Pottsville on down. Lots of mountains in between. Average economy with a couple hundred miles of local travel included on the tank was 17.9 mpg. Overhead is pretty accurate and within about a tenth mpg of hand calc.

On the way home we filled just east of Harrisburg, then headed north on US 15. Again, a mix of just about everything. 182 miles home with an average speed of 60 mph, so you know we were making VERY good time. Overhead read 20.2 mpg for the trip.

Today I did a bunch of in-town travel mixed with a 30 mile round trip over the hills and knocked the overhead into the low 19's. All of this leads me to believe that those of you getting in the 14's aren't so far off the norm... Assuming a good number of starts and stops and considerable shifts. It takes a whole lot of energy to get almost 8000 pounds of truck underway.

One thing did surprise me... All fuel was winterized. I would have expected a couple of mpg's less as a rule. The 600 may be a bit more tempermental than the Gen II's, but driven with constant rpm's right about 2k and she'll either equal or better my '99... And blow the doors off the older truck while doing it!

No smoke on starts, no rough idle, no excess noise... Just a very nice vehicle that draws attention wherever it goes.

By the way... Edge Chip set at Level 1. No need for more!