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Old 29-08-2008, 03:32   #1
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Yanmar issues... white smoke and black oily soot (exhaust) and engine smoke

Hi All,

We're having some issues with a 1977 Yanmar YSB8 single cylinder diesel. There are some wisps of smoke from the engine between the exhaust elbow and the fuel injector. Assuming this was an issue with either back pressure due to build up in the elbow and/or a worn out gasket between the elbow and the engine, we removed and cleaned the exhaust and mixing elbows (they re now totally open) and re-installed them with a new gasket, but the wisps of smoke remain.

As troubling, this season the engine has also been running rough and missing a bit at idle and there is excessive white smoke coming out of the exhaust and a fair amount of black, oily soot appearing on the water and the transom. Assuming that the 2 year old fuel had gone bad, I pumped it out and replaced it with new, but the white smoke remains. I've tried to read up on what may be the cause, but dealing with this appears to be above my pay grade. Two possible issues suggested to me are:

1) Fuel injected into the cylinder is not burning correctly possibly due to:

* Engine/pump timing out
* Fuel starvation to the pump causing the pumps timing not to operate correctly
* Low engine compression/Partially engaged decompression lever
* Water/petrol in the fuel

2) Water leaking into the cylinder possibly due to a head gasket leak or even a crack in the head.

The fuel injector was replaced last year, the head gasket was replaced 8 years ago, she starts quite quickly (assuming that means decent compression), and the fuel is now new. The only obvious thing to me is a bit of a translucent mass around the drain plug of the primary Racor filter. I'm not sure if some sort of growth in the old fuel has partially plugged up the several month old filter and if this could be causing the white smoke or if there is some other explanation that would account for white smoke as well as the wisps of smoke from the engine.
]Any ideas would be greatly appreciated.


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Old 29-08-2008, 03:41   #2

Join Date: Aug 2005
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Boat: Catalac Catamaran
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I have a couple of Yanmar 1GM10's and have seen large amounts of white steam from the exhaust at times. I posted a photo of this here.

White smoke when starting to backup

It only happens when I haven't used the boat for a month or so. When I take her out and run her hard it slowly reduces to a very small amount. I attribute this to moisture accumulating in the fuel tanks. I do have water separators, and the bowls look good, but the steam occurs never the less.

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Old 11-09-2008, 20:26   #3
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Location: Geelong,Vic. Australia
Boat: Columbia 27
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Hi All,
I to have a Yamnar 8 of around the the same vintage, I believe your second suggestion would be the correct way to go,ie replace head gasket! you may even find that the white smoke you see,could be gasses leaking from one of the head studs,as was the case with my engine. Provided you have good access its not a difficult task and the bonus is you will be able to clean any salt build up around the cooling water inlets or ports and check the valve faces for any wear! Good luck,hope this helps?
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Old 14-09-2008, 17:40   #4
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Thank you for the info. The head gasket route is next on my list to try.
CS27 is offline   Reply With Quote

exhaust, yanmar

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