black sooty stuf from exaust

[johns]

does anyone know the cause of this on my volvo md1b this only hapens when the engine is more than half throttle and under load apart from this the engine is fine

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[captainforbes]

sounds like the engine is overloaded. Too big a prop, or poss a fouled prop.
Check the air filter to make sure the air/fuel mix is ok.

Mike

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[dickh]

Check the EXHAUST ELBOW!! This means REMOVING it and checking to see it's not blocked up. IF it's blocked and you clean/replace it, you will be amazed at the difference. See earlier threads on this subject.
Also check fuel filter isn't blocked and needs replacing.

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I'd rather be sailing... /forums/images/icons/smile.gif

 

[brianhumber]

Soot is unburnt fuel so anything that causes it needs to be checked starting with the easy to do items first :
Fouled/damaged prop eg check for knotweed)
Blocked Air filter
Blocked Exhaust
Fuel Pump
Injectors
Compression :Rings/Valve Seats
Increased mechaincal resistance in engine/gearbox/stern tube

with a fair wind it will be one of the first 3, good hunting

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[andy_wilson]

To summarise.

Black smoke is incomplete combustion caused by lack of air or overload.

Has performance changed or is all this new to you.

Eliminate easy stuff first.

Start with engine breathing i.e. Ventilation of engine compartment, air filter, exhaust pipe (trapped or de-laminated), exhaust outlet blocked (seacock?) constricted exhaust elbow.

Fouled bottom, fouled propellor, mechanical friction in drive chain (possibly accompanied by related smells / noises).

Wrong propellor size fitted in the first place.

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[idoltyme]

if it was o.k before id check the injectors to make sure the spray patern in ok and may be get them re tipped

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[andy_wilson]

Injector faults

Poor fuel spray pattern would lead to blue smoke, not black.

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[vyv_cox]

Re: Injector faults

Surely blue smoke is generally recognised as being lubricant burning, whereas black, as others have said, is caused by incomplete combustion. Difficult to understand how poor fuel spray pattern would cause lubricant combustion.

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[andy_wilson]

Re: Injector faults

I agree that blue can be lubricant (which would be apparent to some extent at all RPM as a constant haze) but also unburnt fuel due to poor combustion as in..

Cold start when over fuelling occurs and engine is still cold.

and

Fuel droplets being expelled due to poor injector spray pattern, then the exhaust stinks of diesel.

I think if is gets fully vapourised but unburned it is grey / white and stinks rancid.

Black however remains incomplete combustion due to lack of air for a given fuel charge.

Injectors can be assessed by connecting out of the cylinder. A good injector will emit a gentle 'puff' of fuel each combustion stroke, a knackered one will squirt or dribble, I've never seen one in between so I can't comment. P'raps it's half puff half squirt!!

Anything less than a 'puff' may cause hard starting, but won't cause black smoke.

KEEP AWAY FROM ONE THAT SQUIRTS, IT IS V. HIGH PRESSURE.


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[johns]

i have noticed that whan the engine is heated up the soot seems to clear down to a trickle in the cooling water

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