Getting ready to change the oil on my "new" 03 with 1500 miles on it and am going to go synthetic. First owner changed a year ago (only couple hundred miles driven last year) and ran 5w30 Syntec. The ford manual says to use 5w20. Does it matter that much? I am going to use Mobil 1 or Royal Purple which are about the same price. I am in Southern New Jersey if that matters temperature wise. I expect to put only a few thousand miles ayear on this car. What a great automobile this is!!