revised post

Well, my 2006 Cummins ISX seems to like 1350-1400 rpm, which with 3.42 diffs and .76 top gear tranny, rolling on 22.5 low pro rubber will generally get me a mid 7's year round avg mpg. That has me running between 62 and 65 mph. If I was getting the 5 mpg you would would be comfortable with, I would get rid if the truck. The difference of over $20,000 a year or more in fuel costs would be better spent on a truck that is going to get better mpg. Plus I just turned 750,000 miles on the truck. Still has UOA samples that look as good as when it had 300,000 miles on the engine. Will hold onto this one for quite a while.

 

CHR, are you looking at new truck or used? If new, not nearly enough data on these new motors regarding reliability. And these new motors are all equally complicated. Volvo is leading the class on electronics reliability in the past couple years. They were ahead of the game years ago and had plenty of issues and learned through the school of hard knocks.

EGR is a great example of wait and see. When these motors hit the market the issue was heat. The companies knew this and worked on it. But you had so many company trucks spec'd to run low 60's and governed that many of the issues did not get fixed. Then they are sold and some O/O runs them at 70 in 110 degree heat and a whole new wave of EGR issues pop up. Same issue just not addressed with a recall.

So what is going to happen with these new motors? Who knows. But that is a lot of money for an untested product that could have you sitting in hotel room why un-trained mechanics try and figure it out.

 

A new glider Western Star or Pete with a 6NZ Cat all built to my specs truck and motor.

 

with my '06 EGR ISX in a '07 Volvo 780, with 13 and 3.55 and 24.5 LP, I have seen fuel mileages in the low 9's and once (with a tail wind) broke 10mpg running the flat valleys in California at 58 mph and about 1250. But I am always well under 70K gross. Overall I am in the low 7's, but I do run the higher speed limits as posted in the western states. Little idle time with an APU.

If I had to buy a new tractor today, it would have a Cummins in it. I had previously run 60 series (the smaller 11 liter ones before they raised the speed limits) and a 3406E and C-15.

 

It was the first C15-it's usually in 2000-2003 trucks, although there are some 2003 trucks out there with the MBN serial # prefix, and some 2000 trucks with the 3406E.