26+ road trip
 

Made a run that had about 100 miles of 65~70 MPH speeds up over the pass, then tapered off to 60 and then got hit with some ecomodder fog that got me down to 50.
It looks like I can get this truck up in the mid 20's without aero mods. I hope to see some 30 MPG tanks after the grill and belly pan work.

Congrats! I used to have a '95 F150 with a gasoline I6, and I could never even break 20.

thanks man. It does feel good. I have a louvered grill system on the books, lower and more aero bumper, front dam, and belly pan coming for this rig.
Here is how bad the cooling losses are:
Last night, I came back in 17~23 degree cold. I think my thermostat is stuck. It never got above 145 or so, and the transmission temp was right around 70!!
The transmission fluid circulates through an engine coolant heat exchanger, then out to a radiator and back. In effect, it bypasses the engine coolant thermostat and cools the engine down as well.
I had no cooling fan installed, at all. I left it home.
This rig is designed for worst case high altitude high heat towing over a pass at 20 MPH. The waste cooling air flow is tremendous.
I could have closed off 90% of my air flow last night by my reconing.

Time for the genuine MOPAR winter front.

And of course you can hit mid-20's, that ain't no Ferd.

For what it's worth, I set the cruise control for 1,725-50 rpm. That's the "fastest" slow speed I can run at what is economical. CUMMINS sez the 6.7L is best at 1,300-1,600. 3.42 gears are tempting me once I have trailer spec and other weights (wanting to reserve power, not ultimate mpg as with, say, a 3.21 set) as I'm thinking my rig will always be 18k or lower. Altitude is the potential future problem (but maybe a set of twins, a new cam and EFI Live can come to the rescue).

Look forward to what you find with gauge readings as you go along.

Have you laid out truck spec elsewhere? Tires, gears, weight, etc?

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That trip with the engine too cold?
20.9 MPG!!!!
Ouch!

It had some more 70 MPH on it, but still, I think the cold took it's toll there.

So I cardboarded over 90%+ of the radiator, and went up over a 4500 foot pass on the way home. It went about 5 degrees above the normal at the worst case on the climb.
This was a solid 55~60 all the way, no faster and some slower.
26.3 MPG again :D