Rotella oil has changed formulation?
 

I bought a gallon of Rotella T1. The API rating only shows C, for compression engine, I understand it used to show both C and S (spark engine). Does that mean they changed the formulation? Are you guys still using Rotella?

It's fine. Go ahead and use it. Diesel oil is better. Motor oil producers have had to comply with regulations on emissions...and phosphorus was one of them. The diesel oil still has ZDDP which is said to foul anti-emission hardware on vehicles. The "S" rated oils have less. ZDDP is a major component in the slipperiness of the oil...thus reducing wear. The 10w30 made 10 years ago was better than the stuff we get today...amazing how that works. So I've been using 15w40 in my engine for at least 5 or 6 years...AWESOME running engine.

This is correct. Rotella is not suitable for modern gasoline engines. The Atomic 4 is not one of those!

I am running 5w-40 Rotella synthetic in my A4. :)