Thread: Mercury oil leak upper case

I have a 2013 Mercury 40 hp efi bigfoot motor that has developed an oil leak from somewhere in the upper unit. It's not a major leak, just small drops into the water when the engine is turned off. I check the oil level each time before I start the engine. The engine is not low on oil. I have not needed to add any oil to the engine since I bought it new.

I checked around the filter and there is no sign of a leak around it. I cleaned the housing to try and determine where the leak originates. It appears to come from the side where the vst is located. I can't see any sign of the leak when I inspect the engine.

I have tried to find an oil flow diagram for this engine without any luck. Does anybody know of a site that provides an oil flow diagram for this engine?

Any suggestions as to where I should start in tracking this leak down?

Is there any danger of damage to the engine if it is run with this small of a leak?

You are right, the leak is coming from between the middle unit and lower unit of the motor. I'm not sure why there was oil in the bottom of the upper unit cowling.

But the oil is not milky, it is a light black which is normal.

I am going to take it in for it's 300 hour service. I will have them check it for the cause of the leak.