My son-in-law recently obtained an '02 Taurus SE. Low miles, so it's still under warranty. I know Ford specs 5W-20 for this engine (the 3.0 Vulcan), and that the Motorcraft 5W-20 is actually a Conoco synth blend and has shown some good UOAs on this forum. I'm tempted to put some German Castrol 0W-30 in there instead (found some at the local Auto Zone), however, seeing as how the car is going to Indiana in a few weeks and won't be back until Christmas (and I know the oil won't get changed during that time - if I don't do it, it doesn't get done!) Should I, or shouldn't I?