I have a question to pose to you all. On my '02 I switched to Mystik JT-8 oil around 50K miles. Before I was using Rotella. About the same time my fuel mileage increased by 1.5 mpg. I have been getting a steady 23 mpg since. I haven't changed my driving habits, vehicle loading or the route that I drive most of the time. Could it have been the oil or was the engine just loosening up about then?

I'd be interested in what your thoughts are.

 

The oil will certainly help. When I switched to PB Extreme, I picked up 1 mpg. For the first time since buying the truck, I have maintained good mileage through the winter. I'm only down 1 mpg where usually I'm down 2-3. Oil certainly makes a big difference.

 

A lot of folks have reported much better mpgs after the engine breaks in, as mush as 5 mpgs.
My feeling on the Cummins engine is the type of oil doesn't effect the mileage as noticeably as on a small gas engine. Most Cummins owners have only reported increases of less than 1 mpg after switching to synthetic oil.

 

Hey fschiola, Mystik is some great oil, I have used it in all my tractors, dozers and diesel trucks for over 30 years, as well as my family,ie dad,grandpa for who knows how long, cannot say if it helped your mileage or not, could be the truck settling in and the oil is not going to hurt the mileage. Stick with it as it will do you no wrong. I did not know it was so widley known and used as it is made here in Ok if memory serves. Goodluck,,,,, Rick