Those books were printed 30ish years ago. Modern synthetic oils have come along way. I know people run that Rotella 5w-30 in all kinds of vehicles that don't call for a 5w-30.
I'm not saying it's right or wrong. Just saying that the modern synthetic oils are pretty amazing and they certainly didn't exist when the 3f and 3fe were designed.
On my old 91 I only used the cheapest non synthetic 10w-40 I could find.
well there then
you obeyed the owners manual 10w40 minimum requirements , and had no issues right ?
it's good to know someone cares ..........