bluie5 wrote:
I pulled my Jayco....onboard mileage computer...said that I was getting a little over 12 mpg...It was reading 21 to 23 mpg empty. ....The best I could get towing with the Cummins was 10.5 mpg towing and 19 mpg empty.
What year was the Cummins? Can be the difference in old technology vs new technology. Could also be gearing etc.
Funny thing I've noticed on my '14 Ram with 6.7L Cummins.....I get better fuel mileage (at least on the dream-o-meter) running 80MPH vs 70MPH. This is running empty, not towing.....I would NOT tow my trailer that fast.
I know that bucks traditional thought, but I have a hypothesis as to why. At 80 MPH the engine is running a little under 1800 RPM and at 70MPH it's about 1500RPM. The specs on the engine show that peak torque(800 lb-ft) is made at 1700 RPM. See specs at
Cumminshub.com. So, what I might guess is at that point of peak torque the engine is getting the most bang per quantity of fuel and running at a fairly high efficiency. I could be completely way off base here, but at least it's a rambling thought.
KJ