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Old 28-12-2010, 16:08   #1
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Diesel Exhaust

I have a diesel question.

The last two or three times I've been down to the boat to run the engine, for the first minute or so this black soot looking stuff comes out the exhaust with the raw water. It floats on the surface of the water and doesn't look like oil, but more like soot. I reached down in the water to get some in my hand, but when I rubbed it between my fingers it didn't feel oily. Could that be carbon? I'm not just idling the engine when I use the boat, I'm actually running the around 2,000 rpms.
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Old 28-12-2010, 16:16   #2
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It's unburned Diesel and possibly a little lube oil, both of which contain carbon. After an engine is hot the carbon in diesel becomes carbon based molecules like CO2 that you do not see because this is what the, hopefully complete, combustion is now creating. Also after an engine is warm the oil rings are doing a better job of what they are supposed to do.

Don't worry about the first five minutes, unless your neighbor is giving you the stink eye. Worry about it if this is happening after the engine is all warmed up.
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Old 28-12-2010, 17:59   #3
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Quote:
Originally Posted by David M View Post
It's unburned Diesel and possibly a little lube oil, both of which contain carbon. After an engine is hot the carbon in diesel becomes carbon based molecules like CO2 that you do not see because this is what the, hopefully complete, combustion is now creating. Also after an engine is warm the oil rings are doing a better job of what they are supposed to do.

Don't worry about the first five minutes, unless your neighbor is giving you the stink eye. Worry about it if this is happening after the engine is all warmed up.
The thing I find strange is I've never noticed this before the last few times I've started the engine, so I thought it might be indicative of something more serious.
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Old 28-12-2010, 19:35   #4
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Actually it is all of the above and soot. The soot is unburned carbons. For years I owned a deisel car and if I didn't keep after it the rear end would be covered with soot, especially living in cold climates. Once the engine warms up to normal operating temps the problem is not so bad. This is one of the things the EPA and European environmental agencies have been working on getting diesel manufacturers to do, Reduce the amount of soot diesel (especially long haul trucks) put into the atmosphere.
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Old 29-12-2010, 06:15   #5
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You might consider having the injectors rebuilt. A bad spray pattern can cause incomplete burning of fuel and result in carbon output like you describe.

Also, has it been unusually cold in CA the past few days?

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Old 29-12-2010, 10:20   #6
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We go round and round
What type engine?
How often do you take it "out"

If you are like a majority of sailors......

Power up....leave dock....raise sails

Cut-off engine.........................

Diesels need to be "exersized"
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Old 29-12-2010, 18:45   #7
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We go round and round
What type engine?
How often do you take it "out"

If you are like a majority of sailors......

Power up....leave dock....raise sails

Cut-off engine.........................

Diesels need to be "exersized"
Pathfinder 50

Before this Christmas holiday period I would get the boat out about once a week, and I use the engine more than just getting in and out of the slip. I use between 2 to 3 engine hours each use, and do oil and filter changes about every three months.
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Old 02-01-2011, 07:18   #8
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We're currently on the water- left anchorage about an hour ago. Our starboard engine exhaust is spewing not only water but something that looks like a black liquid - NOT black smoke. It's producing a black film on the boat. It doesn't appear to be oil as we rubbed on it our fingers and it's not oily. We shut this engine down. Checked oil and the oil appears to be very black even though we changed it about 5 engine hours ago. Is it possible this is just carbon? We've never seen carbon coming out as anything other than smoke. What else could it be?
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Old 02-01-2011, 07:32   #9
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Most diesels smoke on startup, and especially at startup and especially in cold weather. My Yanmar 4jh has > 7,000 hours and smokes like a banshee at startup and then clears up when it's warm. No problems with it - it just does it.
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Old 02-01-2011, 08:08   #10
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Well, when restarting and running the engine, it appears that we were wrong about the "liquid". Seems it is smoke after all and it stops when pulling back the throttle a little. Allowing the engine to warm up and we'll see what happens!
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Old 02-01-2011, 08:30   #11
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How bad is it smoking
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Old 02-01-2011, 09:39   #12
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As many have said before. Good fuel and air are the start.
My engines are mechanical (Yanmar 6LY-STE) and have smoked at startup since new.
Mack Boring recomends a cetane improver, it helps
In addition I use a diesel concentrate that cleans and lubricates.
I do not use a bacterial poison as my fuel is always fresh and that stuff ends up in the filter bowl anyway.

After 11 seasons the smoke is less than when new but still there.
The amount of smoke depends on fuel cetane and ambient temperature.
Injector condition plays a factor but that will change slowly.

Spend some money on good fuel and service. Diesels are very durable when taken care of.
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Old 02-01-2011, 13:27   #13
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Thanks everyone for the good advice
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Old 04-01-2011, 14:42   #14
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A friend of mine that is very qualified in gas and diesel engines replied to my question I had about the soot I've been seeing, and I thought I would share it with the group.

"The problem you have is most likely soot. If you have been running the engine lately, you have been sucking a lot of moisture. I know it sounds odd, being a boat and all, but the air is even more saturated with water and this can keep the fuel charge from completely burning, creating soot. When this happened to little old lady diesel Mercedes we would do what was called a "little old lady tune-up". We would take the vehicle out on the road and run it at max (just short of redline) for about 5 to 10 minutes, and it would clean everything out. This problem could also be caused by a missing cylinder, but if that was the problem, you would know it. I doubt that you have anything to worry about. Make sure you are using good fuel, maybe use an additive, like Seafoam, until the rain stops. Let me know if it gets worse."

He goes on to say. "Be careful that you don't get "diesel slobber". That is a term we used in the Marine Corps, but it is a real problem. It is caused by the unburned fuel, the water, and the particulate soot mixing in the combustion chamber and creating a paste. I have seen this **** plug up exhaust manifolds, COMPLETELY, on military trucks."

Here is Seafoam's web site http://www.seafoamsales.com/products.html

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Old 06-01-2011, 18:40   #15
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I think I've solved the soot problem.

I had a couple of things to do on the boat today, and after I did those things I started up the engine. As soon as I started the engine, I looked over the side to watch for water coming out of the exhaust. I noticed that no water was coming out of the exhaust this time, and I was hearing a screeching sound coming from the engine compartment. I quickly went down below to get a better idea where that sound was coming from, and it sounded like it was coming from the front of the engine so I shut the engine down. I now think my raw water pump was making that sound (especially since no water came out of the exhaust), and the soot I was seeing on the water was really fine black rubber from the raw water impellor. I just changed that impellor in September so it's not overdue for changing, but it looks like it is now. I'll inspect the pump, change the impellor, and check for obstuctions.
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