Hm, based on what is presented in this video about oil temps, I'm a bit confused. VW recommends 5w30 or 5w40 (of appropriate specs) in my GTI. Oil temps in the summer are routinely 225F to 235F, which is above the 100C measure point. At these oils temps, the xw30 is no longer a 30 weight oil...so why would I use a 5w30 instead of a 5w40?