I'm using Delo 5w40 and am happy with it. To much stiction with 15w40 on cold startup. I have a 6.0.

 

Mobil Delvac 0w40 here

 

My first oil change was with Motorcraft. that stuff is hard to find. ill be going back to Rotella 15W40.

 

Mobil Delvac 5w-40 Syn in my 6.7 - Jim

 

I use Chevron Ursa 15w40

 

Rotella T5

Was using T6, but I love in Florida. No need to spend all the extra money for T6 since it never gets cold enough here for it to matter.

 

I use Rotella 50/50. 5w 40 and 15w40 in all my diesels.

 

I started using T6 rotella and while it was fine, I just didn't care for it that much. Maybe it was because my truck had a filthy motor and needed the rotella to clean it, I dunno. Overall I wasn't impressed with it, and have preferred the 15w-40 Motorcraft to it. That being said, I've ran the 15w-40 Delvac 1300 it was decent oil, ran Schaeffer's 9000 5w-40 and liked it, but not for that price. Next is 15w-40 Syn-blend Triax that I'm really looking forward to.

Oil Analysis with Motorcraft came back good though so I don't think you can go wrong either way.

-Jake

 

I use Motorcraft 10w-30 year-'round in my 2005 6.0 and it loves it. Runs smoother and quieter on startups and improved gas mileage in city and highway. Started out using Rotella but switched 4 years ago after replacing another set of injectors.