Not a petroleum engineer, don't play one on tv. I've been using the Motorcraft 5w/20 since new with Schaeffer lubes additive and changing every 3-5k miles wthout fail. Oil changes are cheap insurance. I run the dog pee out of this engine to pull my 8k lbs trailer, and it has never used ANY oil between changes, doesn't smoke and loves to rev. 145K as my daily driver and tow vehicle for 10 trips a season. Im not worried about oil so much, but I found out the hard way coolant can be very expensive if not changed under the extreme duty schedule. Very!
