I used Rotella sythetic 5W40 for a time and noticed no change in mileage, noise or the way the truck ran. Also my oil consuption went up to 1 quart ever 1,000 miles. The negated any longer oil changes especially with the bypass filter changes already needing make up oil. So in a 10k oil change I still had to add 10 quarts of oil to keep it topped off. When I use 15w40 rotella I use .5 quart of oil per 1000 miles. I still want to try Schaeffers 5W40 though as that is said to be top notch by a lot of different people.

 

tjbeggs-
This is one of the unusual things about synthetic oil. I have many friends who all report that their oil consumption went up when they used synthetic oil. Everything from 454 engines to heavy equipment they had the same experience as you.
I think that part of the reason for my improvement might be that the 5-40 syn. is just thinner and takes less load on the oil pumps, and that's where the improvement is coming in.
Some of my buddies had external leaks on their engines, and EVERY leak got worse with the synthetic oil. I guess that it penetrates better, or it could just be the lower viscocity thing again.
Every time I think I learn something, it just turns out that I end up with more questions.
Where do you think you are losing your oil? It would have to be either external leaks, piston rings, valve guides, turbo seals, or injector seals, right? I've got a little higher mileage than you but I have virtually no consumption at 6000-7500 mile intervals. What gives?

 

I have no idea really. I am hoping for injector o-rings but I will be doing some stage 1's soon so I am putting it off until then. But I also have some pretty good blowby so anything is possible. no external leaks I do know that.