Does any one know what would be the same in modern times. I have had one guy tell me to run 10w-30 in my 1965 Mercruiser 283 V8 and I Am wondering if formula 4 is code for 40weight or 4stroke. I see that the new quicksilver oil is 25w-40. That makes me think the 4 is for 40weight. What are your thoughts? Do marine engines normally use a higher weight oil than there automotive cousins?
