Using Mercury premium PLUS gear oil

[200090tlry]

Any reason not to use the blue gear oil?

[Sparkieboat]

Any marine gear oil will work. Mercury makes some good oil. I am not sure why they have not started making a synthetic or synthetic blend yet. Some people use the Amsoil synthetic stuff or the OMC synthetic blend. I generally prefer synthetic as it has served me well through the years. But no reason to not use the Mercury stuff it is good oil as far as I know

[200090tlry]

I was told high performace is 100 percent synthetic

There is no smell at all, tacky thick stuff.

[rodbolt17]

actually, yes there is.
Yamaha came out with a GL-5 synthetic oil that is required in the V8 gearcase. (HD LUBE)
it can be used in the 4.2L V6 case.
CANNOT be used in anything else.
so we started asking why.
finally got an answer from yamaha engineering.
the GL-5 does NOT lubricate BUSHINGS correctly.
the 4.2 and the V8 case contains NO bushings.
ALL other yamaha cases DO contain busings some 3 or 4.
if the Yamaha case has a bushing then GL-4 oil is correct NOT GL-5.