I believe the owners manual calls for 50W oil (except in coldest winter). 50W will, of course, keep down the alleged 'sloshing' and 'oil vapors'.
What I can't figure out, is if their use stopped because people found cleaning with kerosene or gasoline a bit too much trouble, or did Fram pay off the car makers so as to have a very profitable business selling paper for 100X what it costs to produce.
Or maybe, the oil filters just didn't fit anymore under the low slung hoods of the 60s....
