# Pitch Black Exhaust Water Yanmar 2GM20F



## rireefguy (May 30, 2006)

So I had some problems with my Yanmar 2GM20F today. I actually first noticed it the last time I took the boat out. The water coming out of the exhaust is PITCH black. Looks like dirty oil, but no slick. I changed the oil last weekend and the oil level has not changed. So I was out today and I was motor-sailing with the engine turning around 2500rpm when I noticed it again. I went down to idle and it goes clear again. Then (at the worst possible moment) the engine started running funny and was only turning 1200rpm at the same throttle position. I tired to throttle up and it bogged down. Ended up shutting it down and sailing home. Additionally, it has been a little hard to start. I dont have anything to base this on as it is a new boat to me and my first diesel but it just seems longer than I would expect, especially when the engine is cold..

Here is what I am thinking:

I think this is a fuel issue. The PO said that he never let it get down to 1/2 a tank, and would always keep it topped off. I now think that he may have been doing this for a reason. (I am currently at just under a 1/2 tank (was going to fill up today but never made it =))

I also thought about draining the tank and will probably still do that if this works.


The plan:

Going to change the fuel filters tomorrow and fill up with fresh diesel. See what happens



Does this sound like I am in the ballpark or am I totally off base. I am kinda new to diesels. If that doesn't do the trick where do I look next, etc.

Thanks in advance!


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## sailingdog (Mar 19, 2006)

the black could be soot, especially if it isn't leaving a noticeable slick.


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## DrB (Mar 29, 2007)

*Sounds like two different problems*

Black exhaust could be soot as SD mentions. If you want to to determine if this is the culprit for the black water exhaust, disconnect the exhaust hose from the muffler and put your finger in it and see if the water in the muffler is black and see if the exhuast hose has any build up in it. If the exhaust water is black, disconnect the exhaust hose from the motor to the muffler to see if that is full of exhaust soot. If so, replace.

The sluggishness on idle/throttle could be related to the black water, but if you have good flow of water out the back, it probably isn't because a significant build up of of soot in the hoses, would result in reduced water flow and water backing up into the motor.

If you haven't changed the fuel filters since you have owned the boat, this could be the cause. A fuel tank that is 1/2 full or less isn't the cause. Do you have a water separator? If so, does it have a clear bulb on the bottom? What color is the fuel in it? If it isn't clear/pale yellow, that could be an indicator of dirty fuel. Changing both the primary and seconday fuel filters could make the difficult starting and the sluggish starting a thing of the past.

DrB


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## Vitesse473 (Mar 16, 2008)

I'd say always start the investigation changing the least expensive items first (fuel and filters). Although diesel is getting almost as expensive as stainless steal (purposeful "a"). But I digress.

How often were you running the motor? Diesel engines do not like to sit for long periods, and while running, like to work hard. If she sat in one place for a long period, or was only used to get out of the marina, then you may have a motor that is protesting lack of use. But, before you go there, you may have water in the tank and fuel lines, and bad filters. Definitely drain everything and replace all the filters. If it still occurs, either buy Nigel Calders diesel book, or rely on some of the very knowledgeable diesel motor folk on this board.

Happy Sailing (not motoring)


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## badsanta (Oct 16, 2006)

checkthe prop for fouling. Also the exaust elbow on the yanmar is a wear item and needs to be replaced at times. Both caused soot in mine.


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## captainjay (Oct 11, 2007)

I am assuming from the port on the stern of your boat you just came out of winter lay up? Checking the filters and exhaust elbow and pipe are both good suggestions. The exhaust elbow will have an area were the water comes in and mixes with the gases, the bend tends to get a build up of soot that severely restricts the exhaust flow. Also look closely at the water area as if it is corroded out it can allow water back into the enigne. Don't remove this until you have a new gasket in hand to reinstall it if it is ok. Also the previous owners warning about not going below 1/2 tank my tell the tale as well. The new low sulfur diesel fuel tends to grow more bacteria than the old stuff. So you may have water and or bacteria or other nasty stuff in the fuel that doesn't burn so well. When you look at your racor is there black stringy stuff in the fuel? If this is the case you may have to have your fuel polished and or the tank cleaned. The process involves pumping all the fuell out of the tank filtering it and then refiltering to clean it up. You can also buy some additives to help kill/fight the bacteria if this turns out to be the case. Start with the simple inexpensive stuff and work up.


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## ughmo2000 (Feb 12, 2003)

Keeping the diesel tank above 1/2, or letting it get below that level shouldn't matter. The fuel is always taken from the bottom anyway. 

I'd check the exhaust elbows for clogging and make sure the air intake is clean.

Good luck!


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## HerbDB (Sep 30, 2000)

I always suspect the last thing that was changed when troubleshooting. Are you sure you did not overfill the oil? This could cause dark smoke in the exhaust, probably bluish tint.


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## JimsCAL (May 23, 2007)

Sounds like a fuel issue. I agree with starting by changing the filters. If they are very dirty and the filter bowl shows signs of water, then changing the fuel is probably next. If the fuel is old and never had stabilizer added, that may do it. If this doesn't fix things, you might need to have the injectors rebuilt. 

Yanmars are hard to start in cold weather since they don't have glow plugs, so that may not be part of the problem.


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## rireefguy (May 30, 2006)

Thanks for all the responses! 

A few more things to add...

The tank was filled by the PO prior to haul and stabilizer was added. He used the boat a lot last season, so the fuel should be pretty fresh.

I have burned 10 gallons this season motoring/motor sailing with out any issue at all.

The oil was filled right to the dot and is still in that exact same spot. (I actually over filled a little and removed some)

Going to grab a filter tonight and take a look... I will update this post later tonight.

Thanks!


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## badsanta (Oct 16, 2006)

How is it in neutral at higher RPM? Does it still smoke? if not check that prop. Something wrapped around it will cause it to smoke. Or a clog in the exhaust elbow will do it also. If it ran fine last week and now it does not that in medical terms is an acute problem, as in a sudden on set. If you did not ad fuel from last time to this, I would change the filters yes but don’t overlook the exhaust elbow and the prop.


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## hbergold (Aug 11, 2009)

Hi Rireefguy

I have the exact same engine with the exact same problem. Did you find what was wrong? Please advice before I end up disassembling the injectors. 
Thanks in advance

Henning



rireefguy said:


> So I had some problems with my Yanmar 2GM20F today. I actually first noticed it the last time I took the boat out. The water coming out of the exhaust is PITCH black. Looks like dirty oil, but no slick. I changed the oil last weekend and the oil level has not changed. So I was out today and I was motor-sailing with the engine turning around 2500rpm when I noticed it again. I went down to idle and it goes clear again. Then (at the worst possible moment) the engine started running funny and was only turning 1200rpm at the same throttle position. I tired to throttle up and it bogged down. Ended up shutting it down and sailing home. Additionally, it has been a little hard to start. I dont have anything to base this on as it is a new boat to me and my first diesel but it just seems longer than I would expect, especially when the engine is cold..
> 
> Here is what I am thinking:
> 
> ...


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## hbergold (Aug 11, 2009)

*Black Exhaust Water Yanmar*

Same problem, any advice from someone?

Greatly appreciated

Henning



rireefguy said:


> So I had some problems with my Yanmar 2GM20F today. I actually first noticed it the last time I took the boat out. The water coming out of the exhaust is PITCH black. Looks like dirty oil, but no slick. I changed the oil last weekend and the oil level has not changed. So I was out today and I was motor-sailing with the engine turning around 2500rpm when I noticed it again. I went down to idle and it goes clear again. Then (at the worst possible moment) the engine started running funny and was only turning 1200rpm at the same throttle position. I tired to throttle up and it bogged down. Ended up shutting it down and sailing home. Additionally, it has been a little hard to start. I dont have anything to base this on as it is a new boat to me and my first diesel but it just seems longer than I would expect, especially when the engine is cold..
> 
> Here is what I am thinking:
> 
> ...


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## cfoxcvg (May 21, 2008)

"hbergold"
Check the Prop. I had only a couple barnacles and it was about 30% of my problem which is the same you are having. See my post on "Cruisers Forum"

Yanmar 2gm20f - Black Water at 2700+ RPM by cfoxcvg

Unless you recently worked on the injector pump then disregard the talk about the shims. It only takes a couple little barnacles on the prop to over work the little 2gm20 but if the prop is clean she will work her but off.


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## hbergold (Aug 11, 2009)

I will check this next weekend. I’ve heard the prop suggestion in other posts, but was lazy to get wet. I checked the mixing elbow (which wasn’t in bad shape), cleaned it, but the black smoke remains at 2700rpm. Will let you know. Thanks


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## jesgatt (Jun 13, 2020)

hbergold said:


> Hi Rireefguy
> 
> I have the exact same engine with the exact same problem. Did you find what was wrong? Please advice before I end up disassembling the injectors.
> Thanks in advance
> ...


Have exactly the same problem. Found a solution for yours please?


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## deniseO30 (Nov 27, 2006)

How old is the boat thereby how old is the fuel tank? in all your endeavors you should also clean the pick up tube and the sludge out of the bottom of the tank. 

Little harder on diesels sounds like you may have a blocked injector IE non-firing cylinder, but I don't know any more than anybody else lol


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## jesgatt (Jun 13, 2020)

deniseO30 said:


> How old is the boat thereby how old is the fuel tank? in all your endeavors you should also clean the pick up tube and the sludge out of the bottom of the tank.
> 
> Little harder on diesels sounds like you may have a blocked injector IE non-firing cylinder, but I don't know any more than anybody else lol





deniseO30 said:


> How old is the boat thereby how old is the fuel tank? in all your endeavors you should also clean the pick up tube and the sludge out of the bottom of the tank.
> 
> Little harder on diesels sounds like you may have a blocked injector IE non-firing cylinder, but I don't know any more than anybody else lol


Hi, The boat is 30 years old, but maintenance was carried out according to specs. The hull and the prop are clean (this also happened when I hauled her in after new antifouling). Both injectors were serviced (by the Yanmar agent) and the head replaced. I also tested them when I put them in place, by running the engine and loosening the fuel supply of each one. The engine began to lower revs for each injector. These are the tests carried out till today:

1. Engine starts immediately.
2. Conducted a compression test (by my mechanic) and the result gave around 400psi per cylinder.
3. Taken injectors for a service and injector nozzles have been changed.
4. Inspected stainless steel exhaust elbow and found out to be ok.
5. Tested engine off load and managed to rev it up to 3400rpm.
6. Inspected water locks and found to be ok - replaced all exhaust pipe.
7. Hulll and prop are clean (even happened after it was hauled in with new antifouling).

Fuel filters have been replaced (found them clean after 1 year). Fuel tank is stainless steel and I never opened it, since fuel filters are always clean after inspection.

Thanks for your reply.


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## deniseO30 (Nov 27, 2006)

"Fuel tank is stainless steel and I never opened it," ... after 30 years.... Think you're going to be in for a surprise! Don't matter what the tank is made out of, aluminum, plastic, stainless, galvanized, they will all get sludged because diesel oil sits around so long in sailboat tanks. 

And all the work you're saying you did and had done reads like you're still having problems beyond filters but I hope that's all it is..


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## jesgatt (Jun 13, 2020)

deniseO30 said:


> "Fuel tank is stainless steel and I never opened it," ... after 30 years.... Think you're going to be in for a surprise! Don't matter what the tank is made out of, aluminum, plastic, stainless, galvanized, they will all get sludged because diesel oil sits around so long in sailboat tanks.
> 
> And all the work you're saying you did and had done reads like you're still having problems beyond filters but I hope that's all it is..


Yes after all the work done, I am still having the same problems. Tomorrow I will open the tank (which is almost full now  ) and will check it out (if possible). I just bough the boat 2 years ago, and according to the previous owner, the tanks was inspected around 5 years ago. I hope this manages to solve the issue. The thing is that at the moment I am experiencing a higher consumption of fuel (I was told that the black water is due to unburned fuel) and fuel filters are clean, that is why I never thought it might be a dirty tank.

Thanks for your reply.


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## JimsCAL (May 23, 2007)

jesgatt said:


> Have exactly the same problem. Found a solution for yours please?


Neither of those guys has posted here in many years, so don't expect a reply from them.

Sounds like you have done all the logical things to try. Overall the engine sounds to be in good shape with good compression and fresh injectors. How bad is the black water coming out the exhaust?. Is it just at startup or all the time? Just certain loads and speeds or all the time?


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## Don L (Aug 8, 2008)

13 year old thread that we still don't know the answer to. :-(


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## Dreadpiratkevin (Jan 23, 2021)

I had a similar issue with my YSM-12. Black water coming out the exhaust at high RPM’s. I finally consulted a very salty and well respected diesel mechanic about it and his answer was- just don’t do that( don’t rev it that high). His words were “sit back, enjoy the ride, if you want to go faster buy a power boat”. 


Sent from my iPhone using Tapatalk


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## deniseO30 (Nov 27, 2006)

It may not be the fuel tank and or pickup, but with additives in the fuel any sloshing will stir it up and it's oing to go; into the filters. 
Almost nobody inspects tanks because it's just too much trouble if they don't have a full size access plate that nobody wants to buy or install into an existing tank.


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