Oil in exhaust, low power

Oct 2, 2008
1,424
Island Packet 31 Brunswick, Ga
I have an island packet with a 1986 3GM30F Yanmar. . While motoring down the intercoastal waterway yesterday I experienced a gradual loss of power. I have Blacksmoke, oil droplets in the exhaust, and an oil leak that is fairly high on the engine block though I am not sure exactly where it's from. The engine still starts easily and runs smoothly.. But when I throttle up to about 20,000 RPMs I can only get another 2000 RPMs with full throttle. In experience a lot of black smoke and oil droplets in the exhaust, scene in the water behind the boat. What are the possible causes. I do not see his addressed in my Book about understanding marine diesels. Also anyone have any recommendations for a diesel engine mechanic in the north Palm Beach area. On the central Atlantic area of Florida.
 
Sep 15, 2009
6,243
S2 9.2a Fairhope Al
I have an island packet with a 1986 3GM30F Yanmar. . While motoring down the intercoastal waterway yesterday I experienced a gradual loss of power. I have Blacksmoke, oil droplets in the exhaust, and an oil leak that is fairly high on the engine block though I am not sure exactly where it's from. The engine still starts easily and runs smoothly.. But when I throttle up to about 20,000 RPMs I can only get another 2000 RPMs with full throttle. In experience a lot of black smoke and oil droplets in the exhaust, scene in the water behind the boat. What are the possible causes. I do not see his addressed in my Book about understanding marine diesels. Also anyone have any recommendations for a diesel engine mechanic in the north Palm Beach area. On the central Atlantic area of Florida.
the very first thing i would check is the exhaust elbow coming out of the exhaust manifold ..going to the water lift muffler

and i think you mean 2,000 rpm's not 20,000
 
Oct 2, 2008
1,424
Island Packet 31 Brunswick, Ga
the very first thing i would check is the exhaust elbow coming out of the exhaust manifold ..going to the water lift muffler

and i think you mean 2,000 rpm's not 20,000
thought about that, but i replaced it last year. when it was clogged i did not get oil in the water (i don't think). however, the yanmar mechanic in cocoa, Fla, did modify the exhaust by putting an extension to lift the elbow "above the water line". i wondered about that too.
 
Sep 15, 2009
6,243
S2 9.2a Fairhope Al
and also check you oil breather tube coming from the valve cover to the air intake and see if it is full of oil ...have you changed oil of late and if you did did you get all the old out and put in the correct amount back in
 
Oct 2, 2008
1,424
Island Packet 31 Brunswick, Ga
and also check you oil breather tube coming from the valve cover to the air intake and see if it is full of oil ...have you changed oil of late and if you did did you get all the old out and put in the correct amount back in
yes, I did change the oil just before we left Jekyll Island. And I checked the oil level on the dipstick. But the breather tube I am not familiar with. I will have to look at that.
 
Oct 2, 2008
1,424
Island Packet 31 Brunswick, Ga
Classic symptoms of a blocked mixing elbow.
well dang it, I should've left the exhaust elbow along. I may not live the yEnmar guy modify it to make it more salt water intrusion free. Certainly could be an issue.
 
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
black exhaust and fuel droplets in the exhaust are signs of not enough air to burn the fuel or too much fuel. Given that the intake is just a big tube and if it had enough air and too much fuel it would speed up I'm thinking that there must be something keeping the air from entering the combustion chamber. if you clog the exhaust you get that. If the exhaust cant get out you cant get air in.
 
Oct 2, 2008
1,424
Island Packet 31 Brunswick, Ga
black exhaust and fuel droplets in the exhaust are signs of not enough air to burn the fuel or too much fuel. Given that the intake is just a big tube and if it had enough air and too much fuel it would speed up I'm thinking that there must be something keeping the air from entering the combustion chamber. if you clog the exhaust you get that. If the exhaust cant get out you cant get air in.
but the droplets are black, i think it is motor oil
 
Oct 2, 2008
1,424
Island Packet 31 Brunswick, Ga
if it was oil i should have mo compression, and run ruff, hard to start? it runs smooth and starts quickly
 
Nov 6, 2006
9,885
Hunter 34 Mandeville Louisiana
Trash on the propeller.. a fouled prop will consume a lot of horsepower and the governor will over-fuel the engine, generating fuel droplets in the exhaust.. the elbow will do the same thing when it fouls..
 
May 24, 2004
7,129
CC 30 South Florida
I'll 2nd Kloudie's opinion on it being the result of a fouled prop. It causes a condition known as overfueling where the air fuel mixture becomes too rich and some fuel burns black and the rest is expelled as unburned droplets. Have a diver clean the prop.
 
Oct 2, 2008
1,424
Island Packet 31 Brunswick, Ga
I'll 2nd Kloudie's opinion on it being the result of a fouled prop. It causes a condition known as overfueling where the air fuel mixture becomes too rich and some fuel burns black and the rest is expelled as unburned droplets. Have a diver clean the prop.
aw come on guys! I cleaned the darn thing yesterday! Have some faith! Haha, but seriously, good idea, but done that.
 
Oct 2, 2008
1,424
Island Packet 31 Brunswick, Ga
New information. When the engine is running hi RPMs under load or when it is first started there pools of black powder, floating on the surface of the water after it comes out of the exhaust. I initially thought it was oil but it seems to be powdery and completely oil free. It is difficult to pick up on your hand or even a paper towel but when I do it does not appear to be oily. Can anyone weigh in on this and where do I start.
 
Jan 27, 2008
3,045
ODay 35 Beaufort, NC
Unburned or rather poorly combusted fuel will be black and sooty and oily. Look at an 18 wheeler blowing smoke for an example. Same fuel you are using. Symptoms sound like unburned hydrocarbons. Follow the advice already given.
 
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Oct 26, 2008
6,045
Catalina 320 Barnegat, NJ
That describes my old 1GM.

New information. When the engine is running hi RPMs under load or when it is first started there pools of black powder, floating on the surface of the water after it comes out of the exhaust. I initially thought it was oil but it seems to be powdery and completely oil free. It is difficult to pick up on your hand or even a paper towel but when I do it does not appear to be oily. Can anyone weigh in on this and where do I start.
I had the same symptoms for years with my 1GM. Mine was over-propped so it (black soot -not oil - in water) would also occur if I throttle'd up more than normal before allowing speed to gradually build. My max rpm was about 2,400 but speed was just over 6 knots at 2,200 with no adverse symptoms (for several years) so I left good enough alone.

What bothered me the most was the black, powdery soot that appeared on the surface of the water at start-up. I took my mixing elbow off numerous times and never found anything that could be considered an obstruction. My fingers would smudge when cleaning it, but scrubbing it never removed any residue, and I never found any build-up of residue anyway. Somebody once suggested that the black residue that escapes during start-up was simply residue left in the water lift after shut-down. Don't know if that makes any sense at all.

To end my story, I gradually lost power over about a season of light use and started seeing grey smoke while operating normally. I pretty much concluded that seals were probably bad ... I had significant blow-by through the dip stick tube and figured my prop size was a cause for gradual decline. My solution was to get a new engine because that is what I wanted. I have the 1GM in the basement, hoping to dive into a rebuild in the near future and see if I can diagnose the problems with a closer look. I'm hoping to recover the engine and donate her to a worthy cause.
 
May 31, 2013
33
Beneteau Oceanis 41 Beaulieu-sur-Mer
I'm with Kloudie1... I had same engine, same issue. Prop was covered with barnacles. Had boat lifted and cleaned... perfect.