I've only got about 700 miles on mine. After the triple-reflash (TSB#'s 18-007-04, 18-004-04, 18-003-04), I went from mid-13's around town/15's highway, to 15's around town/as high as 21 (for miles at a time) highway. Towing my boat (see sig) I am seeing somewhere around 14's ???!!! . . . . of course, those are not 'long-haul' numbers yet.

Tomorrow I leave for Las Vegas (Mandalay Bay) for a few days. I will closely monitor my mileage, etc. - posts to follow. . .

 

I have about 1500 miles on my 600. I'm getting 13 (per computer) around town and 16 - 18 highway with no traffic. Stop & go traffic on the freeway really kills the mileage. I tend to see 14 - 15 in freeway traffic, these are all better then my 3.2L V6 gasser (ok, so it's lifted with mud tires).

I'm taking a road trip from LA to San Diego this weekend. I plan on calculating mpg manually on this trip. I'll post my results when I get back.

-Sam

 

Just over 1000 miles on the truck now.
Got back today from a trip to Las Vegas and back (approx. 580 miles RT).
90% 80-85 mph on cruise control - 10% stop-and-go/city. Several mountain passes. Not much level terrain. High winds. Air conditioning 100% of the time.

16 MPG (plus or minus .01) - hand calculated. Oddly, the overhead was pretty much on the money.

The truck was an absolute DREAM on the highway. DEAD-STRAIGHT, vibration-free steering, the cruise control worked almost invisibly (just steady, silent, SMOOTH modulations of power), even over the mountain passes. Excellent seating for the long-haul drive, especially with the adjustable foot-pedals and adjustable lumbar.
This is a SUPERB truck, and I could not be more satisfied with my purchase.

With just a little bit of restraint, I believe 18's/hwy is very realistic.

 

First tank 15.8 second tank 16.4 both hand calculated. I'm on the 3rd tank now. I hope this trend continues

 

12.2 mpg first tank of fuel
In town driving, to highway speeds up to 96 mph.

Despite some of the questionable mileage, the truck is a dream!!

Rides great too!

--Justin

 

12.2 mpg first tank of fuel
In town driving, to highway speeds up to 96 mph.

Despite some of the questionable mileage, the truck is a dream!!

Rides great too!

--Justin

 

I am about to quit reading these mileage forums. i have never even got 15 mpg empty highway city or towing

 

Got the 555 Think its the same computer Played with it a lot only way its acurate is if you reset with fresh tankful since it figuires AVERAGE mpg from time of reset if I do that at next fillup it is extremely accurate. Always verify by hand. 4x4 sb 3.73s stock 265s first tank 17.75 2nd 19.75 3rd 19.2 4th21.47 YIPPEE

 

Up to 1300 miles on my 600 now, and milage has improved "some" since my first post after the first tank of fuel.

Now averaging right under 14 mpg, for mixed freeway/city driving with no load.

On a 300 mile flat freeway run last weekend (empty), I was amazed at how much difference speed/RPM's make on fuel economy. Going out, 150 miles, it was before dawn and pretty much empty freeway, I ran 80 mph with the cruise control and got 14.4 mpg. On the run back, there was a lot of traffic and I had to run 65 mph (1600 rpm) with cruise control - and got an amazing (to me anyway) 19 MPG!!! Both the 14.4 going out and the 19.0 coming back were hand calculated, but in pretty close agreement with what the trip computer was saying (so far my computer has always been about 1 mpg lower than actual). Just playing around with the speed and resetting the computer since, it looks like this is really how my truck acts - 65 MPH, great milage, 80 MPH (how I really drive, most of the time), not so great milage.

Maybe this is pretty normal, I wouldn't know. This is my first diesel engine. The '98 V-10 gasser I've been driving for the last 6 years just got pretty much the same 11 - 12 mpg no matter how I drove it, or even whether it was empty or loaded - it just always got about the same milage no matter what (with the exception of heavy towing, of course). This new one is a different beast, for sure.

- DAA

 

Good post DAA. I believe you are right on the money with your observations. Look into some 315's if you want the good mileage at 80mph.

You have to keep the engine below 2000 at cruising speed to get good fuel mileage.

It goes to show how misleading these fuel economy threads can be. Everyone thinks they should be getting 20mpg, even if they are doing 80mph in their dually with 4.10's.

The only people really getting high teens and low 20's are guys that keep the rpm below 2000 (which unfortunately is only 60mph).

 

I have just run my first tank threw my truck and hand figured was 15.3 mpg average. That was mostly comuting to work 8 miles one way then sitting all day and 8 miles home. There was a good amount of town driving in there as well. One trip 50 milesround trip and on that was 85 miles round trip. I reset the trip computer for the 85 mile round trip and it stayed in the low 16s the hole way. It looks like it wont be to bad on the hiway but will realy suck in town. I hope to get 1-2 more mpg as the truck gets broke in.

 

Bigblock2stroke,
I drive a dually and do not expect to get 20mpg. My commute to work is 37 miles one way thru country roads never getting over 65mph. There are some intersections (that I must accelerate from) but mostly winding roads. Driving with a light foot I get 13mpg. I have tried AFE,straight pipe,etc., just no box yet. All of this has made no difference in mileage. I use hand calculations and monitor overhead computer. I have not towed anything heavy yet but I am sure it will only get single digit fuel economy.

Once again, I do not expect 20mpg...but when I bought this truck I expected at least 16mpg. I may get it if the break-in sees a 30% increase instead of the 2% to 5% increase that cummins website says is normal.

P.S. I still can't get used to this "clatter" and never will.

 

2004-5 3500 DRW QC AUTO 600. Towed 5th wheel for the first about 100 miles. got home drop off trailer and went to fill with fuel went into the 16's up from 14. It sure loves to pull.

John

 

dwhite,
Drag somthing it wants too.

John

 

jk1364,
What was the build date on your truck? Mine was 01-04-04. I wonder if mine has a problem. If I hear from others like you, I will definetly take it back to the dealer. I had the reflash done (supossedly) and it made no difference.