In
@swatski nightmare thread it was revealed that Amsoil wasn't the preferred oil recommendation by the mechanic. Their recommendation was to stick with OEM. Personally I change oil each season and don't put enough hours each year for it to matter, so I'll stick with yamalube.
Okay, let me clarify a couple of things here.
First, I have and would continue to use the same schedule of oil changes in my Yamaha motors: Yamalube during break-in period and for the first 2-3 oil changes, after that a switch to Amsoil Marine (10W-40).
Second, it was the dealer (not the mechanic) who voiced opinions on the importance of the use of Yamalube - I have heard the same line very consistently from that dealership and other, I believe it might possibly maybe have something to do with them being a Yamaha dealership, perhaps, LOL. Consistent with that, Yamalube offers a separate and pretty gimmicky all time "warranty" if you use their oil and all other maintenance products.
In this regard, in my particular case (the engine making milkshake oil) the dealer's point was more or less EXACTLY what
@BrentEB pointed out too: the presumed anti-foaming properties of Yamalube could save me from trouble I experienced!
When I first looked into the "best" oil to use it seems the 4W has antifoam additives for sustained operation at high rpms. If the oil foams the oil pump(s) can lose flow and the engine will burn up. I'm not going to risk that using an automotive oil! I don't know if other marine oils have similar additives but I don't know how any could be an improvement over the factory recommendation. I'll stick with Yamalube 4W.
Well, the dealer's changed my milkshake oil - mind you - with the thought the use of Amsoil instead of Yamalube being a potential culprit in condensation or some other blow-by or exhaust leak or something type of malfunction leading to "making oil" situation (there are many, many reports of Yamaha outboards "making oil" due to rings not setting properly etc etc, not relevant here, unfortunately). So after the thorough flash and replacing all the Amsoil with Yamalube by the dealership - I took the boat out to test the fix and... quickly made more milkshake within minutes. So there went that little theory - out the window.
That's the story, and after that I have not heard another word about the importance of using Yamalube instead of Amsoil.
Third, I have no way of telling exactly how long the milkshake oil sat inside the motor. Current thinking, TTBOMK, is this is a case of another cracked head. Importantly, after removing the top, the bottom shows no signs of any obvious issues and certainly no indication of corrosion etc.
That last observation makes me think the Amsoil Marine is not a bad deal at all. Would it be any different with Yamalube? I have no idea. I
know it would not be immune to water leak and it would not not-milkshake (due to it's magical anti-foaming properties) as that's been tested. Would the engine components rust? - no idea. They didn't with the Amsoil, that's all I can tell.
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