JFYI, I often use as a reference the actual VW Owner's manual for the Beetle, you can find a copy of the 1952 version here, relevant pages are 7 and 8 "Operatin

JFYI, I often use as a reference the actual VW Owner's manual for the Beetle, you can find a copy of the 1952 version here, relevant pages are 7 and 8 "Operating Instructions": https://www.thesamba.com/vw/archives/manuals/1_52bug.php https://www.thesamba.com/vw/archives/manuals/1_52bug.php https://www.thesamba.com/vw/archives/manuals/1_52bug/3.jpg https://www.thesamba.com/vw/archives/manuals/1_52bug/3.jpg https://www.thesamba.com/vw/archives/manuals/1_52bug/4.jpg https://www.thesamba.com/vw/archives/manuals/1_52bug/4.jpg but at least up to the '70's the recommendations were more or less the same.