Yanmar Diesel Spits Oil When Throttling Up/Down Quickly

[nickroskam]

I am new to inboards and have a 1990 Hunter 30 with an original Yanmar 18hp diesel. It runs great however i notice that when i throttle up or down quickly, usually when docking, the exhaust spits some black liquid out. I would assume this is oil. I have seen other boats do this as well and wanted to be sure this was normal and not an issue i needed to have looked at.

 

[Slow Mo^cean]

If its spitting oil, its not normal. You're engine shouldn't spit oil. However what you are seeing is more than likely just soot built up in the exhaust that gets shot out by water. It looks like oil, but isn't. Best way to tell if its oil is to see if you can see the rainbow "sheen" dissipating from the oil in the water.

 

[Steve Dion]

Nick:

I have no idea how you operate your engine, but you may want to take a look at this link. They (Yanmar) recommends that you run these engines at about 85% of the max rated RPM. In your case that would be 3600 x .85 or 3,000 RPM. We normally run ours between 2,700 - 3,000. I have alway run our Yanmars like this and have not had any issues with them. Just change oil, filters, belts and impeller as recommended it the engine may outlast the hull.

http://www.yanmarhelp.com/operate.htm

PS: I would take you boat out and run it hard for an hour or two and see if that does not clear up your issue. Also review their cool down procedure.

 

[nickroskam]

If its spitting oil, its not normal. You're engine shouldn't spit oil. However what you are seeing is more than likely just soot built up in the exhaust that gets shot out by water. It looks like oil, but isn't. Best way to tell if its oil is to see if you can see the rainbow "sheen" dissipating from the oil in the water.

I didn't consider that. There is was sheen around it, just a black patch when i did it again so I am just guessing its soot. Thanks!

Also, thanks for the yanmar link. I didnt know most of that.

 

[Ken13559]

probably time to clean your mixing elbow.