I was reading the archives and it seems that a lot of people here are using Amsoil, since it's the only "synthetic" 5w-20.
However, their "XL-7500" series isn't a real synthetic.
http://www.amsoil.com/articlespr/article_xl7500.htm
to quote:
"Q: Are Group III basestocks synthetic?
A: Yes, they are synthetic. Group III base oils are highly processed oils and were classified as synthetic in 1999.That year, the National Advertising Division (NAD) of the Council of Better Business Bureaus ruled in a complaint by Mobil Oil Corp. against Castrol North America Inc. Castrol claimed its product, Syntec, was a synthetic oil even though it had used Group III base oils since 1997. The ruling by NAD said Castrol presented evidence that constitutes a reasonable basis for the claim that Syntec, a Group III based formulation, is synthetic motor oil."
This is why they recommend 7500 mile oil changes with here, rather than the 25,000 mile changes with their other synthetics. (Anything over 5K is rediculous if you ask me, even with synthetic).
From the 10W-30 synthetic:
http://www.amsoil.com/products/asl.html
"SERVICE LIFE
In personal cars and light-duty trucks with non-turbocharged gasoline engines: drain oil at 25,000 miles or one-year intervals, whichever comes first."
From the XL-7500:
http://www.amsoil.com/products/xl7500.html
"SERVICE LIFE
In gasoline-fueled passenger vehicles in normal or severe service, change AMSOIL XL-7500 Synthetic Motor Oils at 7,500-mile or six-month intervals, whichever comes first."
What a bunch of crap. Looks like it's just a blend of synthetic. On the 10W-30 they say "100% synthetic" also, which isn't on the 5W-20.
Granted, Amsoil is probably much better than whatever else is out there, but for $5.20/quart plus shipping? There's a 5W-20 blend on the market, in a red bottle (forgot the brand, but it was cheap - found it at wal-mart) - and it's only ~$1.80/quart. Remember though, that a blend could mean 50% synthetic, or 2 drops synthetic.
Let's just hope Mobil 1's working on a 5W-20 for our cars. I always use Castrol GTX, but would rather use a full synthetic.
Cheers,
Joey