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Old 02-08-2013
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Oil in exhaust?

Boat has Universal M25XPA diesel.

Testing a new jib in a minus tide in SF bay the other day, we got up to 19kts wind, but got stuck in the shallows for 20-30 mins. The wind was headed to deeper water, which made it easy getting out. After taking down the sails, the bow pivoted away from the wind and I unfurled a patch of jib. The tide started coming in. Once we got pulled to where we showed a wake and were making about 1.5kts, I turned on the engine and we motored out to deeper water. At some point, I think when I put on a bit of power to 2500 RPM, I noticed dark grey/black stuff in the water exhausting from the stern sea water heat exchanger pipe.

About 10 days prior, I had done all the routine engine maint. (oil & filter, fuel filter, zinc, impeller, clean intake strainer, etc.) and she had tested fine. There was no appreciable sediment in the bottom of the fuel filter.

I cut back on the power to 2000 RPM and the coloration stopped. When I tried to go back up to 2500, the blackish stuff was in there again, and I swear I felt I had less power than normal. So, I stayed low and we motored back through the channel at not to exceed 3.5 kts, when I normally do 6.

We had to run after docking, but I came back the next day and checked the oil level. When I first pulled the dip stick, it was bone dry. However, my experience is that the stick vibrates up a bit when the engine is used, so I put it back in and it came out coated a touch under full. I wiped it off, put it back in, and again got the full reading.

The mud in the bay is blackish dark grey to medium gray in many spots. Crew suggested I was showing mud sucked into the heat exchanger from when we were in disturbed shallow water. However, I don't trust anything at this point except the cost to replace a damaged engine. So, before I do anything more, would welcome pointers to:
1. Can I trust my dip stick? Is there another way to confirm oil level?
2. Can mud really appear through heat exchanger system, being sucked in through the sea water intake? (I've never seen it in the 2 times I've changed the impeller)
3. Why would the grey/black exhaust color only appear at higher revs?
4. Can engine oil get into the heat exchanger and what gasket or other parts am I facing inspecting and replacing?

For reference, I found the following on Wikipedia for generic diesel engines, but not specifically for seagoing:
"Diesel engines can produce black soot (or more specifically diesel particulate matter) from their exhaust. The black smoke consists of carbon compounds that were not combusted, because of local low temperatures where the fuel is not fully atomized. These local low temperatures occur at the cylinder walls, and at the outside of large droplets of fuel. At these areas where it is relatively cold, the mixture is rich (contrary to the overall mixture which is lean). The rich mixture has less air to burn and some of the fuel turns into a carbon deposit."
"The full load limit of a diesel engine in normal service is defined by the 'black smoke limit', beyond which point the fuel cannot be completely combusted. As the 'black smoke limit' is still considerably lean of stoichiometric, it is possible to obtain more power by exceeding it, but the resultant inefficient combustion means that the extra power comes at the price of reduced combustion efficiency, high fuel consumption and dense clouds of smoke".


What I'd love to hear is "relax, everything is fine", but I'll take any expertise you all can provide.
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Old 02-08-2013
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Re: Oil in exhaust?

I think you can trust your dipstick... Check it with the engine off and wait a couple of minutes for the oil in the galleys and lube system to drain back to the pan.

What you saw was probably soot/unburnt fuel rather than oil (or mud, for that matter - esp if you sailed off and didn't churn up any silt with the prop) If the black is unusual - ie - you've run at 2500rpm without issue previously then something may have changed.. but if it's fairly new-to-you and this is the first time you noticed it that's another thing. You might be overpropped, that can lead to what you describe, or your prop could be dirty/fouled and causing the engine to run at a higher load, either can lead to smoke/soot at higher revs...
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Re: Oil in exhaust?

Thanks. Prop is a Gori folding prop installed by pros at boat yard 2 years ago and properly sized for the boat/engine, so I'm told. The engine was cold and off overnight before I checked the oil level as described in the post.
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Re: Oil in exhaust?

You can get this soot when the engine is overloaded - ie finding it harder to turn the prop than normal. So it's possible you fouled the prop at some point with an object, damaged it in your encounter with the bottom, or it's just fouled with barnacles.

My neighbour picked some plastic up on his prop that caused the symptoms you describe.
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Re: Oil in exhaust?

I am with faster^

Trust your dipstick and chances are you were just pushing it more than you normally do (not such a bad thing). You probably cleaned it out a bit.
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Re: Oil in exhaust?

Trust the dipstick.

Overfilling with oil will produce black smoke.

Like said chances are 1 you have fouling of the prop/shaft which will slow you down and make you produce black smoke when run hard, If you were grounded hard and if you ran the engine a lot and sucked up lts of mud its possible you sucked some into the engine, but it should clear.

Look for the simplest first....fouled prop
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Re: Oil in exhaust?

If the engine revs up normally in neutral, but continues to smoke when in gear you should check the prop. You might have something fouled on it, a piece of line, etc.
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Re: Oil in exhaust?

Quote:
Originally Posted by jrd22 View Post
If the engine revs up normally in neutral, but continues to smoke when in gear you should check the prop. You might have something fouled on it, a piece of line, etc.
There's been plenty of it around too. A big ebb stirs it all up, lot's of crap in the water around low tide.
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Old 02-09-2013
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Re: Oil in exhaust?

Thanks to all!
We weren't grounded hard. My son noticed the helm was not responding, and there we were. We sailed into it, then after the rising tide & jib pulled us out to a slow sail, then I turned the engine on. So, I'm guessing there is some 'stuff' on the prop, which would have been folded when we grounded and then pivoted in the mud as the freeboard caught the wind after we took the sails down. I'll try 4 hours of motor/sailing this weekend, and if still an issue I'll have to pay the diver.
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Re: Oil in exhaust?

In a boat, it is important to understand that the load on your engine is tied to your rpm and speed through the water. The load on the propeller determines the load on the engine and the engine will happily run at any rpm unless the load is greater than the power that it produces at that rpm (this is the problem with being overpropped). If the boat feels slower at a given rpm, it is not an indicator of the engine being down on power, it is an indicator of more drag or a less efficient propeller. In your case, it sounds like you were aground so that may well have put more load on the engine. It may well be that you were getting close to the edge of your available power for the given rpm so the engine was fueling heavily which can lead to black smoke.

Gray smoke indicates poor combustion in the cylinders. Common causes are incorrect injectors (this is only a problem for the guys building performance diesels) and a cold engine. From your post, it sounds quite plausible that your engine was cold so that may be the explanation. Black smoke is from overfueling and you don't have enough air to fully burn the fuel. This occurs when you really load down the engine. On older naturally aspirated diesels, this is controlled through a fuel plate normally which controls how much fuel is available at any rpm, on turbocharged ones there is an air fuel control which supplements the fuel plate to control fuel based on turbo boost. If you have a common rail engine, then it is likely that you have a MAF sensor that controls this. This is all a bit off the subject but it controls your smoke producing ability to meet emissions regulations and keep your engine together.

If your boat goes back to motoring at normal speed for a given rpm and you don't get anymore smoke, I wouldn't worry about it. If you motor too slowly, then you should check the prop. If you motor normally and get smoke, then look at the color and try to determine when you get it and someone should be able to help you.
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