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@charlie1932
Did the sheen problem ever go away with more hours? I just got a new boat with twin Verado 300's (just 15 hours on it now) and I noticed the sheen in the water today. Was worried something was wrong and glad to find this thread.
Thanks!
Good morning, the sheen problem occured when shutting down the engine shortly after having started it. The problem went away with more hours. My dealer went through great effort to solve the issue.
There is a bulletin on Four stroke Merc outboards.... Do not store them with the engine in the down position. Oil will sit on the back side of the piston in the bore and pass the rings causing oil sheen in the water on start up.
So trim your engine up a few degrees to allow oil drainage back to the pan.
I have what sounds like a similar problem. When at idle the underwater exhaust just above the lower unit is leaving a sheen or oil slick on the water. I just had the lower unit seal kit replaced after I found the lower unit gear oil full of water. The carrier was split and the dealer resealed everything with a lower unit seal kit. I thought this was the problem, but after that repair I am still seeing an oil slick. Does this sound like the problem you had? How did they finally verify it was the lower crank seal after initially blaming the problem on unburned hydrocarbons?The engine was replaced under warranty, so the engine was not dismantled.