I run valvoline, once I get my rear main fixed I am going to switch to their synthetic. Napa has a real good sale on Valvoline oil around here twice a year because no one wants to run it for some reason.

I can't see switching to the synthetic with the way the seal leaks, but I do want to switch to the lighter weight for cold starts.

 

Somebody correct me if I am wrong but don't all synthetic oils still use petroleum oil as the base stock? That is what I was told by a chemical engineer several years ago. He told me the only place you gain anything with synthetics is in higher pressure and heat situations found in high performance engines. In a basic stock engine it is just money out the window. These engine routinly go over 500,000 with regular oil.

Rick

 

Yes, but it is a more highly refined base stock. The additive package is different as well. If you still change your oil at the same interval as using the dino oil, yes it is money out the window.

 

I am sure my truck ran for years on mineral oil. I changed to synthetic because in my other vehicles I had this purely subjective feeling that when I changed oil, the synthetic was slicker on my hands that regular. And my notoriously cranky Chevy Lumina minivan ran for 200,000 miles with Mobile 1 in the engine, and still was going strong when I traded it in, so I became a believer in synthetic.
Plus, the availability of 5W40 for winter starts was a plus.
I wouldn't hesitate to run on quality mineral oil but I tend to buy synthetic nowadays. The price tag is not that much different.

 

I got that feeling from plain old dino Valvoline oil. That's why I now run it instead of Pennzoil. Never had a problem with not being able to grip a good clean 1/2 inch nut and turn it with any other brand of oil on my fingers- Pennzoil, quaker state, Shell Rotella, Case hy-tran, Lucas, wolf's head.

 

Cummins does not call for synthetic oil. Why do you suppose that is?
They recoomend/endorse Valvoline 15W40. They also make no excetions for syn in their oil change intervals. Dirty oil is dirty oil, regardless of type.
So, I think Cummins is the best judge of what their motors need. Certanily Rotella, Delo, Valvoline are amoung the best choices of named brands. A CI+4 oil(If you can find it) is also WAY better than any CJ (including SYN) for pre 6.7, due to WAY better TBN numbers.
FWIW!