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Old 15-05-2008, 10:03   #1
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Looking for some help and suggestions

Hello, This is my very first post so I hope I'm doing this correctly.
My brother has just bought a 1982 34' Irwin with a Yanmar 3gmd
diesel engine in it, He just sold his 30' Irwin with an Atomic 4 in it.
He is new to diesels. Well anyway he purchased it at a marine
about 600 nautical miles from Chicago, his home port, Last weekend he
took the boat out for a test sail and it sailed perfectly, he had some problems with the diesel. Running below 1500 rpm's all is fine,
running over 1500 to 2200rpms the engine is putting out Black
smoke, he pulled back to idle shut it down and checked the oil,
he went about 1/4 to 1/2 a mile and he used up about 1/2 a quart
of oil. the air cleaner is full of oil. It seems that the crankcase
is pressurizing at higher rpm and the engine is burning the fuel through the intake. When he runs it at below 1500 rpm it is fine.
The previeous owner had the injectors change just before the boat was put in the water. My brother wants to make sure he has a good running engine before bringing the boat on the long journey home.
Any ideas? I'm writing this because I'm the designated mechanic in the

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Old 15-05-2008, 10:31   #2
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Black smoke usually indicated fuel problems. Oil smoke is usually blue/gray. Having said that the oil consumption means your using oil. Sounds to me like compression is blowing by the rings and, as you say, pressurizing the crankcase and feeding it back into the air intake.

Diesels are just 4 cycle engines using timed fuel injection for ignition rather than a spark plug. If you can work on a 4 stroke gas engine, all you need is to become familiar with the injectors (easier said than done).

From here, it sounds like time for an overhaul.

There are a couple of REALLY smart diesel guys on the forum who may give you more detailed and better qualified responses.


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Old 15-05-2008, 11:08   #3
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Thanks, for the info Sunspot Baby
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Old 15-05-2008, 12:38   #4
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The black smoke indicates an air problem (not enough air), and if you have oil in the air intake that could be the cause. I wonder if your crankcase was over filled with oil. If your engine were installed level your crank might be above your sump, but when the engine is angled, the aft part of the crank might be getting down into the sump, and causing the pressurization problem. Just make sure your oil is above the low mark, not to the full mark. On some engines, the difference could be 2 inches or more. Changing the injectors should not cause the problem, but obviously you do have to clean or replace the air filter (try cleaning it first).
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Old 15-05-2008, 13:11   #5
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Randy, at the head of this Forum topic, you will see a sticky titled "Study Hall" go there and you will see a lot of info in regards to this subject. Plus, if you do a forum search using "blacksmoke" you will come up with hrs of discussion on this topic.

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Old 15-05-2008, 13:52   #6
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Thanks for the info.
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Old 15-05-2008, 20:26   #7
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Pat and I and others are more than willing to help you out.

BTW do you know the proper way to check oil in a yanmar?

You pull the stick, wipe it off, insert pull up until seal breaks and push it back in.

Sometimes when you just push the stick in, it will give you a false low reading.

I have seen a number of overfilled Yanmars in my time.
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Old 16-05-2008, 09:08   #8
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Thanks, I will check it that way.

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