Originally Posted by speedysprocket
I run Amsoil Marine 10W-30 full synthetic in my 7.4s now. They make a 25W-40 semi synthetic marine oil to be a direct replacement for the quicksilver, as well. The key with marine oils is they add rust inhibitors for obvious reasons.
If you’re interested in a quote, I can have it shipped to your door for dealer price and shipping is free for $100+ orders this month…
I can kind of understand disregarding the winter weight (e.g. 10W, 25W), but going from a 40 weight to a 30 weight is kind of thin, isn't it?? About the only reason I could think of for that would be running in consistently cold weather.
I assume there is an engineering justification for why the engineers chose that oil weight.