Engine Exhaust Related To Engine Condition

FlimFlamII

FlimFlamII

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Aug 24, 2014
160
Aphrodite 101 148 Coeur d Alene ID
I have a 1980 Yanmar YSM8 with about 375 hours. At least that's what the engine hour indicator reads... Not sure what maintenance was performed by the previous owner. It runs good and starts up okay but when you first start it and give it full power a bit of 'black water' comes out the exhaust. The same things happens after it's been running and you give it full throttle just before shutting it down. While running, there is a bit of constant exhaust smoke. Just wondering what these are signs of and if serious.
Thanks!
 
Tally Ho

Tally Ho

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Jan 7, 2011
5,630
Oday 322 East Chicago, IN
I am no expert, but I think a little black smoke at engine start is pretty normal. I think it indicates some unburned fuel, which would be normal.

If running WOT under load, and you are getting black stuff in your exhaust, it could be a dirty bottom or fouled prop overloading the engine. On my 2GM20F Yanmar, if I run it real hard into the wind and seas, she will have black stuff in the exhaust water.

I am not sure s means she is running too rich and can be adjusted, or I am just overloading the engine.

Greg
 
B

Benny17441

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May 24, 2004
7,174
CC 30 South Florida
What color is that bit of a constant smoke? White bluish is crankcase oil being burnt after squeezing through worn piston rings. 375 hours is nothing for these little diesels but like you say is what the indicator reads. Don't really know what you mean when you say "first start it and give it full power". Diesel engines need to warm up at a slow throttle speed. The black stuff is usually due to unburned fuel. A little bit at startup is of no concern but if excessive then it can point to some problems like a clogged mixing elbow or low compression due to worn piston rings. Put excess black stuff and constant smoke together and it could be a tired engine. Check the oil grade that you are using. An oil too thin can cause them symptoms. Many times a thicker oil can extend the useful life of an engine by reducing smoking and raisin compression. Do check your ambient temperatures before choosing a grade. I would not panic, if the engine runs good and starts fine I would go ahead and remove the exhaust mixing elbow and check it, it could be cleaned or replaced and that should make a difference. Like I said a thicker oil could reduce the smoking. I have nursed weak engines for years with oil and additives.
 
kloudie1

kloudie1

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Nov 6, 2006
10,096
Hunter 34 Mandeville Louisiana
Since he is in Ida-Hoe I would think the fresh water would not make the elbow clogged.. unless, of course, the boat had a previous life in salt water. Sounds normal for start up and maybe a bit over propped (a smidge too much pitch) and or fouling on prop or bottom for the "smoking at speed" problem..
 
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