Trouble shooting black exhaust

[partingclouds]

Almost overnight, while motoring 12 hours a day, the engine oil turned very black as did the wet exhaust. No appreciable difference in oil consumption. Am l wrong to suspect an occluded mixing elbow as a culprit? I'm at a marina and can try to remedy the situation, but could use some advice.

TIA

[Bill O]

What motor do you have? Is it a turbo version?

[partingclouds]

Motor is a Yanmar 2QM20.

[Bill O]

Did you pick anything up on the prop or shaft? A quick dive over the side or an UW camera would tell you if this is the problem?

[SailingHarmonie]

Black engine oil is very normal for a diesel. Not uncommon for it to turn black RIGHT after an oil change, depending on how complete the oil drain is. Certainly black oil would be 100% expected after a 12 hour run.

Sudden appearance of black smoke usually means a sudden increase in load on the engine, or excess fuel. Are you seeing black smoke at all speeds? or only under heavy loads?

Excess fuel could be due to a leaking injector.

Load could be something on the prop, or even a failed alternator regulator putting out too much field current. Have you check battery voltage when you see the smoke?

[rognvald]

Hi, Clouds,
Check your mixing elbow.
Best, Rognvald