Originally Posted By: BrocLuno
Now why would a sealed system internal engine crankcase need corrosion protection? Almost any oil is, by its nature, an anti-corrosion substance ... Yamaha does sell nice oils and I used to run their stuff in various engines. But it is not all that easy to get.
If we are talking about upper cylinder corrosion due to one valve being open to wet exhaust on shut-down, and condensing marine air moisture as it cools, the best protection for that is SAE30 straight grade w/o VII's.
Most modern oils exceed SE, so that's not an issue. NMMA cert does not mean stringent additional testing and I'll bet it's not required outside the USA ...
So what to do if not using YamaLube? I'd go down to the local Napa Auto Parts store and buy their full synthetic 5W-30 or 10W-30 (either will do fine as they are both 30 at op temp) for $2.99 a quart while on sale and run that until the netherworld freezes over
The big deal is to make sure you idle the engine down to let it reach uniform temp as you shut it off. And then to raise the lower unit and and lay it over on the preferred side. If you are really concerned, you can trash bag the lower unit to stop air transfer so that it cools without additional sea air backing into the open cylinder. But there is enough salt water inside the lower leg that will happen anyway unless you completely flush with fresh water every time.
And how many outboard have anyone seen that seize up from corrosion sitting dockside in less that say 6 months of non-use ... It just does not happen. Outboards are tough and they do not have these sorts of issues. The best thing is to run it often
https://www.nmma.org/assets/cabinets/Cabinet456/FC-W%20Combined%20Certification%20Procedure%20Manual%20(3%2016)%201.pdf
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