Merc 9.9 4stk making oil?

[Bait&Sea]

I have a 2000ish 9.9 4 stroke Bigfoot that has been great for many years. Noticed today oil on ground underneath it in the garage. The oil level is way above the high mark on the dipstick. I am assuming its fuel so I checked the vent on boat fuel tank as it feeds both motors, vent is free and clear. I did do an oil change a couple months ago and switched to full synthetic but I'm not sure that that would have anything to do with it. Next I am thinking fuel pump diaphragm maybe faulty. Any thoughts before I take it apart?

 

[AlK]

I would check the Thermostat. I had the same problem on my Yamaha 8 HT. The thermostat was stuck open. The engine was not running hot enough. Changed the thermostat and everything was good.

 

[Bait&Sea]

Ten 4, thermostat is stuck wide open. Thanx a bunch