Smoke from Valve Cover.

[sam.thompson]

Had the boat out for a little fishing and just an enjoyable time.
Cruising down the river and I smell smoke. Not (On fire) type, just know that something is smoking. Opened the engine compartment and smoke was steaming out of the Valve cover vent on top. Only smoked when I was cruising at heavier speeds and RPMs, when gently cruising, it stopped.

1972 Mercruiser 165hp, I/O, inline 6, gm block.

What should I start with to be checking for this issue?

 

[alldodge]

Re: Smoke from Valve Cover.

Do a compression test. If you wind up with weak cylinders then your getting a lot of blow buy and it will be time for a rebuild.