Sierra Gearcase Oil - Gone black quickly

P

pcaker

New Member
I put Sierra Premium Gearcase Oil grade 90 in the gearcase of my 2016 Merc 90 OB, and 2 years later and max 100 hours of running, it is black as coal. However, there is absolutely no trace of metal shavings in the drained oil. I can't understand why it has gone from golden to pitch black so quickly, what is causing the blackness? How concerned should I be? I don't remember this happening with Mercury oil, following similar change interval. When I changed the Sierra engine oil at 2 yr/100 hr intervals, it still looks golden.
 
I thought that stuff was kinda a grennish/blue color?
coorrect me if wrong? I know this new stuff im using for the zuk goes from yellow to a slight green, every oil is differnt depends if its synthetic or semi or normal I can only assume...
Also a tip My mechanic said change all the oils at end of season and put fresh stuff in so you know if there is a problem and your engines dont sit for the winter ...
 
Fixit said:
change your oil every year and you will be fine
Click to expand...
Good advice of course, but still like to know what is happening to the oil? I only cruise at max 3,800 rpm/22 mph. Could exhaust be over-heating the oil ? - though obviously outboard design would mitigate this.
 
Single or twins? My counter rotating side did that for the first 500 hours but now both sides are the same. I use Sierra as well. 1800 hours now.
 
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