With the trend on some new engines to go with a 5w20 oil, I'm wondering if it can protect the engines as well, or is it another ploy to simply get more fuel economy out of the cars to meet CAFE? Has anyone seen any oil analysis data on 5w20 oils? I also notice that a lot of 10w30 and 5w30 oils are dangerously close to being 20 weight oils even when new (such as Mobil 1) and often will shear back to a 20 weight after a short time. What effect will this have on longevity of the engine? I for one wouldn't want to be running a 20 weight oil in my high performance engine.