My 04.5 dually, quad cab, 6speed, with the 4:10s, 4x4, gets 15.5 to 16.5 with the best of 18.02... This SUX!!! All you guys with the 03s, yours is NOT the same engine....

 

Welcome aboard.
I started getting better mileage after about 15,000, I also had the reflash done, and try to keep engine about 2100 rpms, that seems to work well for me, and I am also running 315s, and recalibrated speedo.

 

P.S. on long trips, averaging 70 mph, I can get as high as 18.4, hand calculated.

 

I have the quad race box which has been on for about 2 months. It caused my overhead to read about 1.2-1.5 high. I've been getting consistantly 22-24mpgs hand calculated since winter broke here. I run Amsoil synthetic, red line in the drive train, Howes and MMO mix, and coast where I can. I didn't notice an improvement in mileage when I installed the quad box, but the power is awsome. I now have over 25,000 on the truck and I haven't seen less than 20mpg since winter time. I'll be pulling my 7000# rv in August on a 500 trip and we'll see how she goes. I'm still confused as to how the mileage differs so greatly on these trucks. But I"m very happy with mine. By the way I documented every fill up since new with gallons and miles, and hand calculate to compare with overhead. I also notice that mileage is better traveling 35-50 on local road, rather than 60-65 highway. I think it's an rpm thing.

 

I just got back from an 800 mile trip through Northern New Mexico, and southern CO, over several mountain passes, various speeds. I averaged 19.4 MPG and had a couple hundred pounds in the bed. I'm very happy with that mileage. I do try to keep my RPMs at 2000 or so. From what I've seen, that seems to be the most important factor.

 

My overhead is currently reading 18.2 and since reflash has been very close over and under from a hand calc. Most of the 175 miles on this tank have been to and from town two miles away. I can get 20 and change in ideal hwy conditions driving under 2k rpms. Keep in mind, I drive with getting the best mileage I can. No jackrabbit starts, and at my age I don't need to race anyone anymore. I have noticed that running the ac does have a slight negative affect on my mpg.

 

HMMMMMM Sweet, now that ya mention it I did have the ac on coming back from Bloomsburg, overhead was reading 90deg but since the ez went in I think that is off too

 

Faclondan9570 thats abou what my 03 dually gets.Its a little better then my 1993W250 was with 4.10s.I'm happy P.S. my overhead the FEW times I hand checked was withen .5 of hand.

 

Too much trouble to hand calculate. On two trips to Florida (2,000 miles round trip) I got 18.2 mpg driving 70-75 mph. No other passengers were in the truck and I probably had about 300-400 pounds in the bed. Pulling my 5th wheel camper which weighs about 13,000 pounds, I get about 11 mpg. Around home, with mixed highway and city driving, I get about 16 mpg. The truck is completely stock. I've had 4 diesel pickups and this one gets as good if not better mpg than any of them.

 

I have been told the 600 series (.4.5 to present) saw a reduction in mileage from the previous model; and the second gen. is a reduction from the first. I have been told that the best mileage has always been an old twelve valve CTD (many had 3.55's).

My 05' 6sd. (3.73's) is as follows; around town I get about 15mpg, on the highway at 70 (2000rpm) - 19mpg, at 80 about 14 mpg and gettin' it as much as possible (80 to 95) about 11. Towing a jeep 94' yj and trailer say 5500 lbs. max at 70 I get about 14.5. Thats calculated by hand.

I have heard a third gen. standard output gets better mpg. but it was discontinued in 04.

Just in case you are interested todays CTD have about the same hp and torque of a big rig in the 1970's (no turbo). A late model Volvo rig has about 550hp. and 1800lbs. of torque and gets about 7mpg loaded (I am not a truck driver but thats pretty close). My point is in our quest for speed and GVWR over the last fifteen years fuel economy has decreased.

I would like a 2nd gen. H.O. in my 05' with a 6sd. and 3.73's; that would be perfect.

 

I dumped some MMO and SP in the tank today, and did about 100 miles highway (70-75 mph) with an overhead of 15.4. Not too bad, but still not what I expected. Maybe it's time to consider different gears.

Thanks all for the ideas and comments!

 

I get 24 MPG with my "99" at 60 mph. 20 MPG @ 70mph. 18.5 MPG @ 80mph.

170K and running strong.

 

Jumped in mine the first weekend i had it did 80 most of the way between Dallas and San Marcos. Im now getting 17 in town and 20 if i run just under 70mph go figure on that speed...?

 

If you have 3.73 gears thats about right.It puts you around/at 2000 rpm or a tad less.Put your gear ratio in your sig.

 

I bought the truck used (from a dealer) and if I am correct, it has 3.73 gears. Think I should change to 4.10's?