I have seen 26.6 on the highway amply and running about 70 mph. Not bad for an auto truck.

 

tell us your secrets, I can't get 30 mpg out of my Mercedes 300TDT 5-cylinder diesel at 55

 

3.07 gears, overdrive, and lock up TC.

I get 21-22mpg with 600+ miles to the tank in my utility truck quite often with 3.07s and the 727 tranny. However, I have the blessing of 45 mph roads almost everywhere which drastically helps.

 

I bought my truck,it had sat for 2 years with a 1/2 tank of fuel brakes all locked up on it,tires square lol put some get the water out additive in there and a de bug fuel additive in it topped it off and blasted it home 6 1/2 hours runnin 70 to 75 mph across Wa. state and got 19.4 mpg.I was amazed especially beeing new to these trucks...I love my 1st gen CTD! I havnt checked mpg since,but soon I got another long road trip to make at the end of the month.

 

Guys, JQ is running a double OD also. 47RH and a GV...

 

I was getting about 21-23 last summer, running about 70, in 100 degree heat on my way to ND. I'm going to swap out the bumpstick and see what I can get running a tighter converter, gear vendors, and keep my 2500 redline.

I should have data on 55 for hours on end next winter. I plan on running two lanes most of the way back to Toledo when I go back to visit PA.

The cylinder deactivation cuts the oil to the hydraulic lifters, allowing them to collapse and not fill the cylinder with air. I think it would take some serious oil gallery re-engineering to make it work on these. Some computer installation/programming, too. Plus, you would immediately be running less manifold pressure, when you dropped two or three cylinders, dropping power and probably requiring that the other cylinders be reactivated.

IHC tried cylinder deactivation in the 70s with the 1468 and 1568 tractors. But they cut the fuel under light load to 4 cylinders, and I guess they sounded like they were ready to blow up til you put a load on them and it fired on all 8 again. There was a way to disable it and I guess most of them had the work done. It didn't save much fuel, but it was all mechanical, so it was still pumping air in the unfueled cylinders.