My manual for my 2018 mercury 150 pro xs 4 stroke recommends 10w-30 for general use but says I can use 25w-40 synthetic blend oil too. What are the advantages of each of these oils? I never go out unless it’s 50 plus degrees out and it rarely gets over 85 where I fish. Will the 25w-40 protect the engine better? Interestingly the manual specifically states not to use full synthetic oil.