Re: 0w30 synthetic yay nay?
I did run Mobil 0W30 once, but didn't buy it again because its so overly expensive overhere.
0W30 should be a perfect oil. Cold it has a viscocity of a straight 0 oil (and cold it is in fact still too thick for perfect lubrication, but much better then any 5 or higher grade oils, since the oil flows a bit easier and the oil reaches earlier the lubrication points, so lowering the startup wear, which is by far the biggest wear factor on an engine.)
At operating temperature it has a viscocity of a straight 30 oil, which is the required one for our 4.7.
Here in Brazil the jeep stealers do run 0W30. (at least the one where i go to).
I don't know why jeep doesn't recommend this oil in the manuals, instead of the 5W30.