I had a '90 model 5.0 (302) making over 300 hp & tq to the rear wheels. Drove 1500 miles and changed to
synthetic (Mobil One). It did not leak nor could I see it burning
oil but it used qt to qt half per 1000. I changed back to dinosaur
oil.
My rule is; if the motor was build by the manufacture to use
synthetic oil, then use
synthetic oil. If not, use the oil the motor was designed to use.
Dwight