Black gunk leaking from prop

[markh28]

1975 Evinrude 115hp

I know there is normally some gunk that leaks out of the lower after running the motor (unspent oil, exhaust, etc), at least there is on my other motors. But this stuff looks more like black tar to me. When I changed the water pump I noticed the inside of the exhaust housing was coated in it. Its almost like someone ran a bunch of STP through it. It leaves a nice black stain on my driveway. What can I do to clean this motor up?

 

[Bob_VT]

Yes, it is unburned fuel and oil mix. I have cleaned it from my V4 and it is just the way things are. You could try to switch oil brands and see if the sludge changes or lessens. I have used degreaser, kerosene, soap and water which all worked you can do what I normally do and live with the nature of the beast.

 

[emdsapmgr]

It's possible that the engine is running cold. If the thermostat (the vernatherm on your engine) is constantly open, the engine will run cooler than normal. Cold combustion is poor combustion and will promote the tar/sludge problem. That engine's vernatherm is a low temp device anyway, permitting the powerhead to warm to only 115-130 degrees at idle. If it's stuck open, it could be even lower at idle. Check the powerhead temps with a laser temp gun so you can determine if it's operating at the factory spec temps.