Group, I am thinking of making the move from Mobil1 5W30 EP to GC 0W30 for my 99 300M w/102k. What I was thinking for an OCI was 10K with filter change at 5K. I know the filter change may not be necessary, however...it would give me piece of mind, and certainly wouldn't hurt the oil. From what I've read on here, the 0W30 is thicker than 30 when warm. Which is what I want. But is there that much of a difference between GC 0W30, and 0W40??? I am going to use a Wix filter for the media, either the 51515, or the 51773. I am contemplating this change from Mobil1 because from what I've seen here, the EP5W30 seems to thin out when hot. Not good when racing. I don't race all the time....but in the Spring, and Fall...it gets ~ 100 passes total. Any thoughts??