just changed out my 3.7l dodge from havoline 5/20 to a mix of 2qts 5/20 and 3qts of 5/30 motorcraft synblnd. the engine rattles more @ startup (?piston slap,timing chain?)but it is super smooth when warmed up and especially at high rpms where as with the 5/20 havoline it was kinda of harsh and seemed to vibrate more over 4000rpms. pp 5/30 is the only thing that has made it quiet @ start up? i dont get it?????? anyway, do you think the motorcraft is ok to 5000 miles?