Go here and read High-Ten's post toward the bottom.

Great info from Cummins and may help explain the bad mileage people are experienceing.

Great info!

https://www.dieseltruckresource.com/...983#post418983

 

It may explain Cummins's procedure for break-in. But that has nothing to do with mileage. The best you can hope for is perhaps one mpg better after your engine is seasoned. This idea that your milage will be significantly improved with use is a myth.

There is either a problem with the 600 or cummins has just given it enough extra umph to make a significant decrease in economy.

All the guys that think 13-14 mpg out of a CTD is good, haven't, IMHO, experienced the real pleasures of cummins economy.

2cents

 

I was refering to this paragraph:

MID BREAK-IN PERIOD. After the first 1000 miles, the engine is ready to be worked, which will help seat the piston rings to avoid blowby and avoid carbon buildup to avoid fuel slobber because of light load operation. If possible, drive in hilly or mountainous areas OR load the truck with 700 - 800 lbs OR pull an empty trailer (tandem car-hauler type)*.


I assuming the term "slobber" refers to the guzzling of fuel.

If nothing else it goes to show it can take many thousands of miles to achieve maximum fuel milage.