Here's <a href="http://forums.audiworld.com/a8/msgs/75960.phtml">Why</a>, and note that this is NOT the easy to find Mobil 1 0w-30.

Mobil's <a href="http://www.mobil.com/USA-English/Lubes/PDS/GLXXENPVLMOMobil_1_Racing_0W-30.asp">Product Describtion</a> says that 0w-30R been discontinued, but I'm not sure that it's really true (race guys would still want it). It is getting harder to find, but I believe it's still available from <a href="http://store.avlube.com/mo1r0wraoil.html">AV Lubricants</a>.

0W40 is vw502 approved. 5w30 is not. That said I ran 5w30 in my biturbo S4 ( a much tougher application) with excellent results - my turbos were mouse-quiet* while others' were failing.

Grant

* I find this expression odd. Have you ever heard mice in the walls? Sound like demolition teams

I just picked up 2 5-L pails from my local indie. He seems to like it. Specs are surprisingly similar to M1 0W40.

Grant