Yanmar 3ym30 excessive black smoke

[Graeme Colmer]

Replaced fuel filters, air cleaner good, fuel appears clean, motor starts easily, approx 250 hours on motor, good water flow out exhaust.
Motor blows out heavy black smoke and puts heavy black soot out onto water
Looking for experienced suggestions what to do injectors , coolant elbow?
Ideas thoughts appreciated.
Searched previous forums no clear direction.

[Jentine]

Diesel engines are simple. They require metered fuel and wide open air for proper operation. If either of these factors are altered, the result is incomplete combustion which is black or white smoke. Check the air intake to ensure it is clear. If so, remove the injector nozzles and have them serviced. They can be rebuilt for a fraction of the cost of replacement.
There are other possible problems such as a failure of the injection pump and/or improper timing but they are less likely.

[Jon Neely]

Could be exhaust elbow being clogged. I have seen yanmars with under 100hrs do that, stock ones seem undersized on most models.

Sent from my SAMSUNG-SGH-I747 using Cruisers Sailing Forum mobile app

[Graeme Colmer]

Sincere thanks
You've given me a starting point
GC

[Graeme Colmer]

Today pulled out the water exhaust mixer bend and found it very nearly blocked corrosion and carbon
Cleaned it out as best could reassembled and restored full revs no carbon no smoke beautiful however condition of bend is likely needs replacement in next 12 months and I was told bronze replacements can be obtained. Would anybody have any ideas where I may be able to obtain such? Appreciate any advice anyone might have
Thanks

[DubeJ]

Hmm, I am getting white smoke (very little) from my yanmar. I am going to be taking the steps you did already GC, and hopefully all that everyone has suggested, at least take a look at as well. I will take pics and upload/share with all of my upcoming mistakes and probs! Haha

[boatpoker]

3YM30's had an issue with inadequate heat exchangers on engines with serial numbers between 00001 and 05565 although I think by 09' you'd be out of that range, still it's worth a check. See attached service bulletin ....

[SkiprJohn]

Did you find the propulsion threads?

[olepedersen]

the yanmar 3gm's heatriser is easily cleaned. Remove from boal. heat up with a torch,when good and hot hit with a big hammer all scales and soot will fall out Ole