In my son's 1984 and my 1986 owner's manuals, for other than extreme duty, the 4.9L calls for an oil and filter change every 7500 miles, while the V8s are scheduled for 5000 mile intervals.

I wonder what the Ford engineers knew?

 

IDK, but I do know that my family ran the f100 & F150's w/6 cyl and I had one also (1990 bought new) for 16 years....we always changed the oil out every 3-4K miles.