When I put the "new" Engine in my car, I plan on putting Mobil 1 in itfrom the beginning. I've been using Mobil Syn Blend 10W30 in my current 4.6, and it starts up fine in 4F weather. The consensus I've read is that Mobil 1 10E-30 will be fine for Long Island weather. The other thing is I read the Article I found posted somewhere on this board, and it states not to use Synthetics for the first 2000 or so miles. The engine was listed as having either 1 or 1000 miles on it. Looking at the inside of the engine, I don't think it's got 1 mile, but it could have 1000 or less. Should I just put the synthetic in, since most of the break in is done at this point?