My wife drives around 18,000+ miles per year in her 2005 Explorer with the 4.6 engine. She uses synthetic for the 2x yearly oil change. My 2002 F-150 only goes about 5,000 miles anually so I use Motorcraft 5W-20 once a year. My 1996 Contour, mainly our long distance vacation car sees 8,500 mile OCI's or 2 years on Schaeffer 700 SynBlend. Will try G-Oil next, great coupon, will check to see the used oil analysis on this site to help determine the OCI.
Whimsey