Yesterday I headed to the lake with my friends boat in tow. His boat is just an 18 foot fourwinds. The weight was probally around 4000 lbs. My truck averaged around 12 mpg on the way updoing 55 mph. On the way back I was getting around the same mileage when I shifted the tranny into 5th. My milage shot up to 17 mpg according to the overhead and stayed there all the way home doing 50mph.

I will hand calculate when I fill up.

 

I've heard of this on some friends of mines gas trucks...

 

I have noticed that i get better mileage with the truck at 2200 RPM's up to 2600. On my 5.9 around 2000 or less was my best mileage. Ive tried it both with my truck and the higher RPM's seem to do better mileage wise than the lower.

 

It could be a combo of the engine liking the higher RPM's and also at 50 MPH you had less wind drag on both the truck and boat.

 

Fuel mileage should be a function of pedal position in these trucks. It's been my experience that keeping it floored in OD at 1800rpm will yield worse mpgs than running it in a lower gear at 2600 rpms with the pedal 1/2 way down (my truck is older, but same principle).

 

With the varible vein turbo or whatever the turbo is called on these motors IJMO my Cummins just seems to pull fine in either 5th or 6th gear over-drive and the mileage hand calculated figures the same. The over head showed a difference LOL- go figure

Now I have lots of seat time as I run a route of 400-500 miles a day and five days a week in this truck. I have 48K as of 8-17-07 and It just seems to me the problem is with the higher RPM and using 5th gear OD you gain the ability of the higher spun turbo to help get all the emissions through a very very restrictive exhaust.

You use 6th gear OD and you slow the motor down and get better effiency, but then the slowed down turbo fights harder to push all the exhaust through the exhaust system we have been force feed on these little trucks...

So the two choices of gears to use have been a wash for the most part, at least for me. I get 10 MPG pulling on a moth average and it does this in 5th or 6th gear...

The interesting part is the truck gets 12 MPG running empty, which is not at all what I would expect running empty and just seems to me that shows just how much truble the motor is having with the exhuast system.

Maybe I am wrong about all this, but there just seems to be a tremendous level of technology under the hood of this truck for this level of fuel mileage and the fact that running empty or pulling a 27 foot gooseneck trailer loaded real heavy yeilds 2 MPG difference LOL...

I don't even see much difference in the mileage when running really hard either and by hard I mean way in the throttle and pulling the trailer 90-95 in either the 5th or 6th gear OD... Is really impressive about this truck is that she will drag the trailer like that and effortless. Really is one strong 'ole motor and sure appears to me that all she needs is to be set free of all its sensors on the exhaust and intake area's and then open the exhaust on her...

Mine sure seems to be held in place and I bet the oil company's just love this setup