I was going through some things I got from my grandfathers garage when he passed about 12 years ago. Thought this was interesting, it has a copyright date of 1960.
Quote:
SAE20/20W. ..... It was very common back then for cars to use light single weight oil.
Trucks, too. My father-in-law's Ford F600/700 gas powered trucks were serviced every 3,000 miles with 20/20W back in the late 60's/early 70's and worked well for several hundred thousand miles.