I think that the owner’s manual on my 1954 Buick called for 20W-20 oil in moderate climates. I know I used this oil in the spring and in the fall. In the summer I used straight 30 weight,and in the winter I used 10W-30. I haven’t owned the 1954 Buick since 1965. My brother does own a 1954 Buick that he restored, but uses modern 10W-30 in the car.