Thanks for the input. In short synthetic oils are not reclassified due to extra refining of fossil oil. That is a MYTH, plain and simple, folks.
Please read: http://www.amsoil.com/frequent.aspx
Cut and pasted-
Q: What types of synthetic base oil fluids does AMSOIL use?
Answer: As the developer of the world's first API qualified synthetic motor oil in 1972, AMSOIL has gained more experience than any other oil company in formulating automotive synthetic lubricants. It is this extensive experience that provides the ability to maximize product performance through use of a full range of high-performance synthetic base oils, most notably polyalphaolefin (PAO). AMSOIL views synthetic base oils the same as it views additives, with each having its own set of unique properties. AMSOIL engineers its lubricants with the synthetic base oil or combination of base oils best suited to a specific lubricantís application demands (gasoline, diesel, racing, transmission, gear, extended drain, extreme temperature, etc.).
AMSOIL INC. maintains an unwavering commitment to provide products that outperform the competition and deliver maximum benefits to all AMSOIL customers. Performance is the bottom line.
Again, there are tons of misconceptions about oil, I am NOT the end-all in answers, but do know a fair bit, and when I don't, do spend the time to find out. I do not rely only on Amsoil as a source of information, however they are very forthcoming with tech info and do not appear to play smoke and mirrors like most conglomerate oil co's do.
Luckily one does not need to know much about oil, just use what the factory recommends, pretty easy, eh? Sure that works...for awhile.
It may not meet the needs of your engine for your operation conditions-- extended storage, low annual mileage, extreme temperatures, extended idling, proper turbo lubrication (and prevention of 'coke' deposits), changes in oil and fuel formulations over the decades, excessive oil changes and waste, extra cost and time. I'm in no position, nor want to be forced to deal with mechanical problems. I've seen enough in gas engines over the years, including my own, to know that not all oil is created equal, not even close. Poor quality oil causes excessive sludge buildup, excessive crank case acids, which in turn attacks seals, allows more blow-by which in turn wears seals faster due to carbon buildup, that accelerates oil leaks-- and more work/expense than it's worth.
From what I understand the DD engine was engineered in 1938, with varying changes in manufacturing and metalurgy over the decades. I've been told by several old timers and bus nuts that our engines are very tempermental and survive best when run hard and not to idle them to avoid excessive temperature drop that will cause more carbon soot, which is bad for the rings and oil.
I'm happy to report that my 8V-71N still has clean oil even after using it this summer (unlike my first DD with fossil oil, completely black after minutes; good engine: started at 38F on its own), climbing the Cascade Mountains and using the Jake Brake most of the way down. The bus started up one cool day last week, after near freezing temperatures during the nights, with nary a sound of it turning over. Push button, engine starts and runs, faster than you can read those four words. I like that