Prime - What speed to get the best fuel mileage

55-60 for mileage, then I leave Cali and its 70 -75 cuz I can

 

There is no single best speed. A lot of factors are involved; not the least of which is the engine in your truck. Every engine has a unique torque/speed/fuel consumption function. You just need to find out where the sweet spots are for your truck.

You can find that on a flat road, the best mileage is 58 going one way, and 63 going the other. Why? "Flat" does not mean "level"; there are many roads that are flat, but very few that are level. Wind is a factor, too. Going into a 10 MPH headwind at 55 needs the power of running 65.

If your truck doesn't have a real-time MPG indicator available, a good indicator of fuel consumption is the turbo boost gauge. More boost = more fuel being used. (And don't be alarmed if the boost goes up when the engine brake is being used; you're not using more fuel.)

 

I have had the most success with 1250 rpm and rarely pushing more than 15 psi of boost. This is with the DD15. With the 3.36 rears this puts me right about 57-58 mph on the flats. I'm seeing an average of 8.6 mpg for this summer.

 

1250 RPM's huh? Is that engine even running?

 

Take a look at the DD15 power curve. It has a very flat curve with it peaking right around 1210 rpm @ 1550 ft-lb. You don't need 450 hp to run the flats even at gross.

 

I get it....But at 1210 rpm's you might as well remove the engine and attach a sail for wind power. It's not what is needed but rather what is tolerable and for me 57 mph is intolerable. If you have to run that slow to make a profit it's time to raise your rates; but that pretty much sums up Prime for ya. That's for another thread though so I'll leave it at that.

 

Personally, I don't need to run that slow to make a profit. I run that slow to make more profit. With the way the appointments are usually set up, it makes no difference if I'm an hour or 3 hours early for delivery.

 

Ever think it's their trucks. Been running heavy last 2 months all over country and still maintaining a 7.7 at 65. Prime must have poop trucks.

 

There really isn't any set formula like right now I have a 43,000lb load coming out of Idaho and I have been running 65mph the whole way back east across Wyoming and Nebraska and I am averaging a 9.5mpg. Now if I turned the load around and went back west there is a good chance I would not even get close to that 9.5mpg. Now I have been I. The Northwest the last two weeks and except for this load have kept it around 58mph and last week I pulled a 9.4mpg and this week I am at a 9.5 for the week.