Yanmar 6lpa-stp 315hp traces of black smoke

[IslandLife]

I own a 2007 Ocen Runner 2900 with a Yanmar 6lpa-stp 315hp motor. I began noticing small amounts of black smoke and soot on the stern of the boat. It eventually got worse to where a short 3 mile run at cruising speed still gave me soot on the stern. Took it to the mechanic and showed him some pictures of the exhaust while running at cruising speed and right away he could tell something was wrong. Said it was dumping fuel. I also lost my top end speed and rpm.

The engine was removed from the boat, fuel pump was removed along with the injectors and sent to a yanmar shop. Results came back that the plungers on the delivery pump were bad, sending too much fuel in result. The fuel pump was replaced (brand new). the filters on the injectors were replaced and re-calibrated. The mechanic also removed the head which was full of carbon and took it to the machine shop to be cleaned. The intake valves were pitted around the edges so he replaced them with new valves as well.

Once put back together and take for a test run. Engine runs great! I am getting good cruising rpms as well as WOT rpms at around 4,050rpms. But there is still a small trace of black smoke and soot on the stern just from a short run. We then changed the fuel filter as well as clean the charge air cooler. Did another test run. Same result....... good rpms, but still getting the small trace of black smoke and soot on the stern.

WHAT TO DO NEXT??? Any other ideas would be gratefully appreciated.

[N4QC]

Ideas:

1. Has the turbo charger been cleaned?
2. Is there adequate air available in the engine compartment? If the turbo is creating a vacuum effect in the engine compartment, then an addition fuel source to the engine might be from the air intake manifold system, sourced by a leaking supply and/or return fuel lines around the injectors. A vacuum could also cause crankcase oil to be ingested from a poor seal of the valve cover or from the crankcase breather. A vacuum condition will tend to dry up any wet spots on the engine so that you don’t see them. Run with the engine compartment hatch/cover open in order to provide maximum air supply and then check for wet spots around the engine.

Adequate clean air and clean fuel make for a clean running diesel engine…

Happy hunting…

[IslandLife]

Thanks for the ideas. I am going to clean the stern today because right now I can right my name on the back with the amount of soot that is there. And that was only from a 7 mile each way at cruising speed. I have to run the boat to the mechanics Shop so I will run with the engine hatch open to see if that makes a difference. I will also pass on your notes to him as well.

Thanks

[RobS]

I will run with the engine hatch open.

Thanks

Don't forget ear protection for you and crew, you WILL need it.

[RobS]

I think this is your boat? Where is the air intake venting to the engine compartment around the center console?

[IslandLife]

RobS, I think you are faster than google at finding stuff. Yes that is the boat. The air vents for the engine room are at the stern of the boat. There are none on the engine hatch itself.

[RobS]

The stern? Maybe because these were originally fitted with outboards.. Seems to be inadequate fresh air ventilation to the engine in my opinion but you say this has just now become a problem? If the air supply was minimal or marginal to begin with and for some reason has now become restricted that could be your issue. Has there been any cause for change in the effectiveness of the existing stern vents? It appears it would be simple enough to cut in some vents around the front and sides of the console if needed.

BTW, I'll be in the Caymans in October.

[IslandLife]

The boat was purchased from the previous owner in 2007 with the current setup that is there now. He has had other issues before but not this particular issue with excessive soot which started a lil more than a month ago. The boat is at the workshop now and the mechanic is taking off the charge air cooler and the elbows on the turbocharger to check for any blockage. I do agree some more vets on the side of the engine cover would be a good idea, just don't understand why air supply to engine room may be an issue now when it hasn't been for so many years.

First time visiting? Whats the reason of visit if you don't mind me asking.

[RobS]

just don't understand why air supply to engine room may be an issue now when it hasn't been for so many years..

I agree 100% and that's why I asked if it could have become restricted. Some storage items blocking the vents, flex duct that has been flattened out or kinked, etc...

First time visiting? Whats the reason of visit if you don't mind me asking.

Yes 1st time visiting. Wife's 40th birthday. We are both divers.

[IslandLife]

I have asked the mechanic to do a test run with 4 people on board which was the load i had yesterday, but do the test run with the engine cover open. I am also curious of doing two separate test runs. Clean the stern off, then travel the same distance at an rpm before the turbo starts to spool (probably 1800rpm). Then clean the stern again. and do the same run at cruising speed when the turbo is spinning (around 3000rpm). Could that help determine if the turbo is lagging? I will keep you posted on the results.

Awesome!! That will be a fun trip. Diving is great here, I dive myself but not frequently.

[RobS]

I have asked the mechanic to do a test run with 4 people on board

I hope he doesn't charge you his labor rate times 4

Can't hurt, the more conditions and test you do the more info you will have to prepare your diagnosis.

[IslandLife]

Yes exactly, Im trying to eliminate as many possibles causes as I can. Im wondering how much more can be left. I will find out the latest from the mechanic around 3pm.

[IslandLife]

Ok, so I went by the mechanic's shop yesterday. Informed me that they, removed the entire racor filter assembly as well as the secondary fuel filter on the engine. They also removed the charge air cooler to check for any dirt or restriction in there. Put everything back together and ran the boat wih some new diesel from a small gas can. He made a bout 3 test runs as well as one more with me on board. The engine ran great and surprisingly AND Thankfully the exhuast was majority steam and minimal black smoke. I left the mechanic's shop and ran back to my dock about 6 miles more before I checked the stern. very very light mist of soot, the least I have ever seen. So I think I am headin gin the right direction. Could be those fuel filters, could be the fuel in the tanks. I will get some new fuel this weekend and monitor the performance.

[jleonard]

There is always soot in the exhaust of a diesel engine. When mixed with water it will deposit someplace, and due to the station wagon effect it deposits on the transom. The faster you go (to an extent) the greater the effect.
Many boaters add an extention to their exhaust fitting putting the sooty mist farther from the boat. This minimizes or may eliminate soot on the transom.