Mpg question (optimual rpm)

Winter fuel?

 

Usually 1250-1300 Rpms are the best for fuel mileage if you’re driving plains with no head wind with light loads (different weight for every engine and rear axle ratio) in warm weather. if any of these terms change you might have to adjust your rpms so you don’t lug your engine and downshift constantly.

 

Don't trust the MPG display on your dash. Keep track of the miles between fill-ups then calculate it yourself. I think you'll find a difference. I have the same truck with the Cummins engine and the display MPG also dropped recently, but when I calculated it myself, it was much better than what the display said.

 

You might be right with your rpms. Friend of mine sent me a picture of his 2016 peterbilt with 12.8 packard engine 10 speed manual dashboard last week. Both Pete and KW are manufactured by packard so your truck is probably geared the same so 1100-1150 is good.

 

You're seeing the switch to winter fuel (less btu's in #1 diesel). Fuel gets blended based on the calendar, not based on ambient temps.

 

I'd check your owner's manual and see where the green rpm band starts.

Typically the green is the peak torque with the lowest amount of HP.

My Cummins is 1250 at the minimum. I typically run at 1325 for max mpg, without beating up my engine.

 

Paccar