My friend recently put Amsoil 0w-30 S2k into his 2003 Vette. He has noticed that his engine temps are now 20 degrees cooler and his oil pressure is more stable. He previously had factory fill Mobil 1 5w-30. Why would a thicker oil (then M1) create cooler engine temperatures? My initial thoughts are that it transfers heat better due to lower friction. I've guys with Audi's say this too that Amsoil 0w-30 has reduced their engine temps. by 15 degrees on average. What is interesting about this is that Amsoil buys there PAO base stock from ExxonMobil. Are their various grades of PAO base stocks and would they be selling out better base oils then what they are using in Mobil 1? On the other hand, it could just be the added package and the fact that Amsoil is a more refined, expensive therefore better product. Any ideas?