18 mpg Dodge while towing?

JIMNLIN wrote:

azdryheat wrote:
Friend claims 18 mpg while towing 35' toy hauler with 2003 Dodge Cummins Diesel with manual transmission. He says he never goes over 55 mph. Is he for real?

I have a same '03 Dodge/Cummins NV5600 305/555 HO 3.73 axle 2wd in a 2500 short bed quad cab truck.

19 mpg while towing a heavy TH ???
...could be a single best tank using the short fill method.
....... watching the fuel guage and guessing at mpgs.

A '03/'04 305/555 Cummins HO does get some of the higher mpgs. Mine has averaged 12-12.5 mpg (pencil figures) over several tanks on long trips pulling my 11000+ lb 5th wheel trailer.

My truck in sig. I've found over a dozen "comps" of others with '03-'04 CTDs pulling Airstreams and vintage kin cousins (as I have) where mpg is 14-16 without really trying. A travel speed range of 55-65 and comps made for non-hilly terrain. This is with TT's from 28-35' and 7-11k in weight.

Manual transmission and 2WD bump it that much higher. I was averaging 15+ at 62-63 mph with a previous identical trailer. This truck, solo, DOES NOT fall below 24-mpg highway (58-mph @ 1,725-rpm) rain or shine, loaded or empty, night or day, traffic or no traffic . . and I've seen 27-mpg numerous times in the South Central U.S. (Order of importance for mpg is: truck spec, climate, terrain and then driver).

So, while 18 is really up there, lets remember that the close "fit" of a 5'er to the truck is a real aerodynamic aid (if that is the trailer type). The air gap on mine is over five feet from truck tailgate to TT front and this is contraindicated for mpg. An aero trailer is pretty well mandatory. So with a squared rear (drop door) and high ground clearance I have my doubts about 18 as anywhere near consistent (the average, not the high of a few tanks).

My truck is also stock. An aftermarket custom tune (Smarty UDC) could well bring my average (21-mpg past 42k miles; 50/50 town or country) up by another 1-2 mpg. Indeed my goal is to hit 17 towing for the conditions conducive to mpg (above).

The only other truck turbodiesel close to an early HPCR CTD is the very first Duramax.

So, a clean sheet combined rig of an early HPCR CTD and an aero 5'er (1989 AVION; 9500-lbs empty; 14k gross) could well hit 18-mpg, IMO. The correct rig and a motivated driver. (As a professional driver I bring tools to the subject of fuel economy that pay. It is more than just slowing down, it is understanding how the tenths of a mpg add up or drain away, Trip planning is central).

Moderator edit to re-size picture to forum limit of 640px maximum width.