I have a 2003 Cummins 5.9 engine with 150,000 miles on it and change the oil every 7,000 miles (including all of the filters).I use dino oil only and it still doesn't burn a drop of oil between oil changes. I have had two other Cummins diesels in a commercial fishing boat that had 5,500 hours on them when I sold it, only used dino oil in them as well. Neither burned a drop of oil.I have a CAT engine in my DP RV now and only use dino oil. Both CAT and Cummins will tell you that they don't recommend synthetic or not recommend it and they both will say that synthetic does not change the oil change intervals. If you want to use synthetic go for it!
