So, I am using this 0W20 stuff now, I have to admit it is nice. The oil seems like it circulates instantaneously, etc.
However, I was doing some reading which suggested that 20W oil used to be used on new engines to help cause slight metal-to-metal contact between pistons and cylinder walls, essentially breaking the engine-in. This is not such a big deal with newer engines that have tighter cylinder clearances. However, the old Jeep 2.5 is likely no poster-child for tight cylinder clearances
As such, I might stick with the 0W20 for 5-10,000 miles, but at the next change go to a 0W30/5W30 or higher to put a little more lubricant between the pistons and cylinder walls. May even give the Amsoil Synthetics a go (since this is supposedly a true synthetic and not derived from forms of petroleum, unlike Mobil 1 or Castrol)
Note: Course, some say that modern 0W20 synthtic is a different breed from the old 0W20 break-in oils: it flows great, takes the high heat, doesn't get to thick at temperature, thus minimizing drag. Still a very thin oil, but no metal to metal occurs This 20W "engine-wear" issue seems to be an ongoing argument on some boards out there, typically ford mustang, race car sites.
