With the right truck it is do-able at a reasonable speed.

I have seen 27.1 and 27.2 mpg on two recent trips. Never less than 24 mpg. The terrain is flat, and -- if there are no headwinds or heavy crosswinds -- above 26 mpg is easy. "Easy" assuming that this kind of driving is no longer new, it is not "work" anymore; one has already learned from the professionals:

http://www.heavydutytrucking.com/2004/10/078a0410.asp

And the famous "Cummins White Paper" .pdf

http://www.everytime.cummins.com/***...Whitepaper.pdf

Truck should be properly spec'd (signature)

2WD
NV-5600
Highway rib tires (stock Michelin LTX)
Bed topper (tonneau cover better; less rear vacuum and sail area.)
Factory rake (important; I experimented with a torsion bar Chrysler years back and it matters)

The past nearly 10,000 miles I am averaging 23 mpg for all miles due to frequent round-trips of just over 600 miles with limited miles in each city at either end. Truck is usually above 8,000-lbs. With U-Hauls biggest enclosed trailer: 19 mpg.

All miles at 1,750-rpm, or, 59 mph (GPS-corrected). Going slower saw no increase in mileage, any faster and it fell off quickly.

Nearly half of this route is 65-mph, and the other is 4-lane with low traffic. Easy to run either 5 or 10 mph under.

I've seen posts by others reporting the same with similar trucks and terrain: long distance commuting on familiar ground.

My stops are preplanned (I know them in advance: I can glide in and out of them), they don't change, now, and mentally one knows the road and the times so that makes all decisions automatic. The driver -- in other words -- never changes his deep attention to road, load, weather and traffic conditions and is making the tiny corrections as needed. Same as when I was an OTR route driver.

No lane changing, no braking and mild acceleration gives one the edge to obtain those last few high numbers. For example, when I traverse Houston East-West (or reverse) I know exactly what lane to be in at what point; where traffic can or will impede me, etc.

With a tailwind the entire way I'd break 28-mpg, but the geography is such (Texas Coastal Bend) that predominant winds change at one point.

I don't have an airspeed indicator, but I know the corrected reading for the overhead and that tells me about drag on any given trip. (An airspeed indicator and boost gauge -- worked in tandem -- would allow speed changes to reflect reality).

http://www.aircraftspruce.com/catalo...rt_miniasi.php

I printed off a chart showing fuel consumption versus boost. THIS IS THE KEY COMPONENT TO HIGHWAY ECONOMY (posted by "Moparman73" [name?] a few years back). 5-lbs was one magic number . . . . I can't find link now. Curve dropped like a stone.

What too few realize about a diesel (versus gasoline) is that the motor knows what it wants. Your job, as driver, is only to be the eyes the motor lacks. You work for the motor, not the other way around. Keep it happy and those tenths will climb.


As to modifying the truck I believe the tow mirrors are NOT a problem (likely on Fords they are), but closing off the upper grille openings to smooth over-the-hood airflow

http://www.truktoys.com/modelView.aspx?id=47

and closing off the bumper (all areas beneath body color strip: foglight openings & center opening; as if you "banded" the chrome/balck plastic area completely) would give the best bang-for-the-buck (and be easily changed for towing and/or hot weather). Same with a deepened front spoiler.

https://www.dieseltruckresource.com/...2&d=1236308946

Running A/C makes no difference. I have had mine maxed for many of those trips.

In short: no idle time; all miles between 1700-1900 rpm; highway speed just below 60 mph. Only shifts above 1900 are fourth and fifth, and then only to 2100 or 2200 rpm (progressive). Off the cruise control when changing lanes and time every single [potential] maneuver to avoid using throttle or brakes.

 

I was working in Yellowstone Park when the park was closed to the public. The speed limit was reduced to 35mph and I had more than 50 miles to drive in the '03. I set the cruise control at 35 in 5th gear. Engine was turning 1500 rpm.

I reset the overhead just to see what it would show. 28mpg. At that time the overhead was always within +-0.1 with hand calculated.

May not be accurate but 28mpg is possible. Just have to drive a lot slower but not safe on our highways.

 

Some of this stuff I forget about. I've been driving for economy for over 36-years. My father and grandfather were two of the best drivers I have ever seen, and I was lucky to learn from them starting in the early 1960's. It was all about time versus distance and what trade-offs were acceptable. For example, cruise control in the 1960s on a big block was lucky to maintain a 4-mph variation. You might be "set" for 66-mph, but you'd see anywhere from 71 downhill to 62 uphill. True, we could pull a 440-4V Dodge to 15/16 mpg at 57-8 mph by not using the cruise and watching the speedometer like a hawk, but it was WORK. We used the CC and "fell" to 14 mpg for most solo driving in the 55 mph years of the '70's. Worthwhile trade-off. The high compression 440's were a joy. They were relentless (kind of like the CTD) and "flattened" every hill on the trip.

In hilly terrain, as good as the Cummins CC is, it is obvious that one can do a better job, BUT as the CC is so "tight" otherwise it isn't worth it, IMO, when solo for most routes. It is an assertive program, and I think it fantastic. Solo, my truck won't even slow down on most rises here in Texas and I am overcoming the gassers

so I have to be prepared ahead of time to go around them; OR, cancel the CC so I don't run out of a verrry comfortable braking distance [my usual choice].

Second is how to pass. I so rarely see it done properly that it is worth an explanation:

On a two lane highway and I am approaching a slowmover, I come off the cruise quite early, maybe a quarter-mile (no exaggeration) as I don't want to change throttle position at all if possible; just take up the slack.

To pass I want

to do ALL my acceleration in my lane, and, as I pass the slowmover I am actually slowing down as I pass the point of the drivers position to glide back into the lane once I can see his front bumper in my center rearview mirror. I want to use the minimum safe passing speed AND I want to hit that number as gently as possible while still in my own lane.

If you were riding with me you might not even notice I had passed someone (given a light load and long sight lines with no real opposing traffic). Otherwise, I'm puttin' 'er back in the big hole as I pass the driver and I'm heavy. THAT is the "point" at which I am aiming (cause if something goes wrong I can stand on them and glide back in behind the slowmover).

In other words, I am hanging pretty far back before that decision is made. A lot farther than most of you realize (because I have to watch my 6 o'clock for the cretins who try to pass me), so there is some pretty fair throttle work (all minor) to maintain the position I want.

I HAVE TO KNOW MY ACCELERATION DISTANCE in order to gauge things. I want to out of "rocket boost phase" BEFORE I enter the oncoming lane. (An exaggeration, unless I'm heavy as the carpet and my accelerator pedal are barely acquainted).

My attention is way beyond the slowmover, as far as I can see (and to the rear). I only really register his vehicle [or combination] in peripheral vision once I make the decision to pass (not the action thereof).

The cruise is back on once I am lane-centered.

Same with Interstate passing. I am early into the left lane -- CC cancelled -- and maintain a 5-mph headway. Again, not noticeable to a passenger otherwise distracted.

But, for fuel economy purposes, it is still better to run under the limit as the cretins all bunch up in packs trying to run above it. Just learn to use the mirrors and some slight defensive maneuvering to herd them around you. This is huge help while towing.

If it's a big truck and he doesn't have much headway, come off the cruise and let him in by dropping about 10 mph once his front bumper reaches your tail lights. It's simple to e-a-s-e back up just under the CC set speed to Resume.

Etc.

28 mpg is do-able with the right spec truck and the attitude of skill acquisition.

Smooth. If I maximize being lane-centered then all else comes easily.

 

Just have to drive a lot slower but not safe on our highways.

That's a rationalization I see quite often. I, too, would like to make a long trip in Direct at 47 mph or so. But I see this offered as a "reason" not to maintain slower headway in discussions about towing and/or economy. Show us the proof, I say, as I've covered more miles than I can count in a truck speed-governed to 55 mph and NEVER had a problem, much less a citation or warning. The Interstate minimum is 45 mph. Guess who'll be at fault in a rear-ender?

I, too, don't like a 15-mph variance between posted speed limits for trucks and cars, but 10-mph is EASILY workable for economy.

The fools who drive above 70 are already over their skill levels, and the burden is on them. There is a LEGAL REQUIREMENT to recognize the 25-mph speed variance possible between any two vehicles AT ANY TIME or AT ANY PLACE on the Interstate system.

Besides, better to practice now versus than when fuel hits $6.50/gl. (Or other dire scenarios). I know there are men who could "embarrass" me with their skill, and I want -- every time I get behind the wheel (the great lesson when young) -- to be better than I am. Especially as I am past age 45 when skills obviously decline. Bad habits are hard to break, but good habits are gold.

My father -- who never got less than 90,000 miles out of a set of brakes when I knew him -- started driving in 1939. He recently had to have the car taken away since the Texas DPS found it impossible to fail him on driving tests that the medical profession had deemed a legal requirement. Funny as hell from one point of view, that those by-the-book DPS troopers (several of them) couldn't fail this old guy with senile dementia. Pleasant as could be, just couldn't remember their name.

We sort of just "stole" the car one weekend. You already know the bumper sticker: When I go, I want to go like grandad, peacefully, in my sleep . . . not screaming like his passengers.

 

i say its possible, but not with anything near stock. my recient road trip from Seattle to Los Angeles i hit one stretch of I5 south where i got 26.2 MPG inbetween fillups. 65mph with cuise on. i think once i get twins and injectors i should hit 28-30 along with playing with programming.

 

I got 36 mpg one time... It was on a long trip and I was coming down a winding hill.... I noticed the mileage on the lie-o-meter was climbing so I quickly reset it and grabbed the camera so I could PROVE to naysayers that it was possible to get 36 mpg, but while reaching for the camera I glanced out the window and noticed I had inadvertently driven off a cliff and THAT was why my mileage was so good....

YES we all can get great mileage, and I get 17 all day long with 425 hp, but that 17 is an average between downhill 30 mpg and uphill 12 mpg. So change whichever parameters you need to make yourself happy... Always drive slow, downhill or only in the sun..... Or change your gearing and put air foils on your tailgate, roof top and tie rods.... Whatever!

If you want a real downer, pull a 12,000 pound trailer through hill country using winter blend fuel.... Now where's your economy???

 

If you want a real downer, pull a 12,000 pound trailer through hill country using winter blend fuel.... Now where's your economy???

You mean it's worse than behind a 1973 454 4.10 geared Chev 1-ton?

Some of us spec'd these for economy: low fuel bill and long life. Deadhead miles (empty, non-working, non-paying) need all the help they can get.

 

Hey I had a 460 Ford with a 4.11 rear that I pulled an RV all around the country.... 5.5 mpg average. YEE HAW!!!