Smoking Yanmar

[Dean Strong]

The Yanmar 2GM20F in my 1990 Hunter 30 is driving me crazy.

In 2007 the mixing elbow coked up, I pulled it, cleaned it, and reinstalled it. Since then, the engine starts smoking after about an hour at cruising RMP (2850-2900, 80% of max rating), and leaving an ever present soot stain on the hull after of the exhaust port.

At idle there is always a slight soot discharge visible on the water surface (on return to port).

I've run tests to make sure the 3 bladed prop is the right size. I get 4100 rpm in neutral, and 3750 in trials, achieve hull speed of 6.7 knots.

At the end of last season, I had a mechanic pull and rebuild the injectors, and adjust the valves. At the same time I pulled the mixing elbow again, it was half blocked, and replaced it.

The engine runs at normal temperature--I can always touch the mixing elbow even after hours of hours running, our cool Northwest waters keep it just warm to the touch.

The engine runs well and consumes very little oil between annual changes. I had the oil lab tested this spring and all is normal. The engine has 700 hours on it. I never idle for prolonged periods or run at low RPMs; always at 75% to 80% of max rating.

Its not the elbow, not overheating, not injectors, not burning oil, not overpropped, but still emitting unburned fuel.

I think about just running it, but I know the elbow is getting clogged, and slow but steady damage may be occuring to the pistons and cylinders.

Diesel experts, please tell me where to go next with this.

 

[petersea]

What color is the smoke ?? black, gray or white ?? are u saying the visable discharge you see is fuel ??

 

[Bill Roosa]

unburned fuel means too much fuel or to little air. sounds like you have eleminated the fuel from the equation. Too little air can come from not being able to get air in or get exhaust out. check your air cleaner, air heater if installed, and exhaust hoses and muffler. That is about the only thing left.

 

[Dean Strong]

The smoke is gray colored, but is probably black, just not very thick. I know what white steam looks like from overheated cooling water discharge, and blue from oil burn. I had the oil analyized to be sure water wasn't somehow leaking into the cylinders (black + white = gray). This is clearly unburned fuel. At startup, when it puffs (normal), there is a soot discharge on the water surface. After motoring for lengthy periods, when idling before shut down, soot discharge is barely visible on the water surface. You have to look carefully, but it is there and should't be.

I did replace the airfilter when the injectors were rebuilt.

Any other ideas? Anybody have a muffler that clogged?

 

[Benny17441]

We had a similar problem on our 2000 2GM20F and ended up replacing the mixing elbow. We had cleaned the original one but somehow it did not do the job. Now you have had this condition for a while so it could be very possible for that soot to be restricting flow inside the muffler. If the problem persists check the prop for balance or damage on the blades. Lastly check the performance of the water separator and the condition of the fuel. It is indeed a mistery that the problem seems to surface just about an hour into cruising. Temperature/compression issues? Did you own the boat at the time or do you recall when the problem started? When was the three blade prop installed?
Go back and review everything one more time, sometimes we may ovelook something. Good luck and please let us know what was the reason when you find it.

 

[petersea]

Did the mechanic who changed the injectors check or change the injector pump timing ??? Did the problem happen after the repair work was done or was the work done to try and fix the problem ??

 

[Dean Strong]

Great ideas. Since you guys seem to be interested, here is all of the data:

3 bladed prop was added when I purchased the boat in 2001. The engine had only 500 hours on it. The former owner had done something to blow up the engine, so it was new---one reason we bought this boat. There were no smoking issues until the first time the elbow clogged. But it was overdue, as elbows need cleaning or changing at 300 hours. I went 580 before having any problems. Here is the rest of the log maintenance:

08/27/07 580 hrs - Loss of power and rpms, mixing elbow blocked solid, removed, cleaned and reinstalled.

06/20/09 588 hrs - still smoking, sea trial (for prop overload check) at suggestion of local Yanmar dealer (Seattle).
4100 rpm in neutral at dock
3750 rpm, 6.7 kts over water, 6.7-9 per gps, three north/south runs off marina, calm flat water.

07/16/08 591 hrs - Prop (15 x 10 3 blade) Cleaned, Checked balanced,(Prop Shop), removed 1/2" from edge.

07/03/10 688 hrs - motored 3 hours to overnight, returned 7/4 severe smoking on exiting harbor; shut down and sailed into dock at home port. No further problems for next 5 hours, but never motored for over an hour.

07/16/10 693 hrs - Diesel Systems rebuilt injectors, adjusted valves.
07/17/10 693 hrs - Owner pulled mixing elbow, 1/2 restricted, replaced.

05/26/11 725 hrs - oil analysis, Spectra Lab, 50 hours on oil, fuel dilution, total solids, water content, viscosity antifreeze all normal.

06/24/11 754 hrs - smoking after 1 hr. @ 2950-3000 rpms, reduced to 2700, less smoke, hull soot stained (cleaned).

07/17/11 768 hrs - smoking after 1 hr @ 2900 rpms, reduced by 100-200 rpm, slightly less smoke, hull soot stained.

The fuel is clean. I installed a port on the tank right after purchasing the boat because mold was growing in the fuel. I drained the tank, cleaned it till a white rag would wipe the surface without being soiled, and installed a Racor primiary filter. I repeated this process when the smoking started.

The only new suggestion I've recieved is to check the exhaust back pressure---to pull the elbow and examine the exhauste manifold for blockage, and do the same for the muffler.

 

[kloudie1]

Interesting.. Don't overlook the hoses to and from the muffler when ya go in to check the muffler.. The soot is unburned fuel..since it is heat related (only smokes after running a while), it may be something related to the injectors (maybe even just one) not sealing correctly after getting thoroughly hot.. Was the engine completely replaced or was it a short block that had the old injectors and high pressure pump added from the damaged engine?..There are some critical settings on the pump that balance the amount of fuel injected between the cylinders. If this is wonky, one cylinder can overheat and do strange things.. Unfortunately, it starts getting expensive to pull things and test them at a specialized shop.. If the air and exhaust passages are clear, then ya going to have to start getting into the fuel controls to find why it starts injecting too much fuel after heating.. Probably safe to continue to run but if ya back off on the RPM a little until you find the problem, the excess fuel won't be as bad for the rings and cylinders.. Don't motor in excess of 3400 RPM.. and verify the tachometer so that ya know what the rpm really is.. The motor will smoke a good bit if run under load at 3750 since its fuel delivery system is not designed to run there ..

 

[petersea]

Found some interesting and hopefully some helpful info so I did a copy and paste with credits at the end to the publisher, I also agree with above posting that you RPM are pretty high 4100 in neutral is about 400 to 500 high as well as 3750 under a load is high neutral should be in the 3600 to 3700 max range and WOT under a load should be 3300 to 3400 with a "cruse" about 2800. You maybe have to have the pump settings checked IF the tach is really correct so may want to verify the tach readings first.


BLACK smoke ..

Black smoke is the most common emitted from diesel engines and indicates incomplete combustion of the fuel. Black smoke causes can vary widely and include ..

Incorrect fuel injection timing ... only applicable if it has been changed from its factory setting. Yanmar engines do not "loose timing".
Fuel injection pump wear, or incorrect settings.
Incorrect air/fuel ratio ... dirty air filter
Dirty or worn fuel injectors .. commonly carbon deposits affecting spray pattern.
Carbon deposits in combustion chambers .. common in lightly loaded engines.
Excessive carbon build-up around exhaust valves and exhaust spaces.
Sticking piston rings .. often due to carbon deposits.
Glazed cylinder cross-hatch .. due to carbon deposits.
Incorrect valve clearances ..
Faulty valve stem seals .. rarely.
Engine wear in general .. often misdiagnosed when carbon deposits are the real problem.
Engine oil viscosity too low .. check oil grade against operating conditions.
Cool operating temperatures .. coolant should reach 85C, or higher. Check thermostats.
Engine overloaded .. reduce load, use lower gear,
High altitude operation .. lack of oxygen to complete fuel burn.
Dirty or restricted air cleaner systems .. air intake filter partially blocked.
Poor quality fuel.
Black smoke can occur across the entire operating range, but is usually worst under full power. Black smoke should be hardly visible in a correctly running engine.

Obviously, worn or damaged components must be replaced .. the earlier you identify and fix the problem, the less damage will be done. Keep on top of engine tune issues, including valve adjustments, regular servicing of air, fuel and oil filters. Do not buy fuel from suspect outlets. Dirty engine components, such as fuel injectors can be easily restored to full cleanliness by using an effective and reliable fuel system cleaner.


Black smoke is high in carbon or soot, which is an undesirable product of diesel combustion. The combustion of diesel is a complicated process of breaking down the various hydrocarbon fuel molecules into progressively smaller and smaller molecules, by extremely rapid burning (explosion) in the presence of oxygen. The main and ideal end products of combustion are CO2 (carbon dioxide a greenhouse gas) and water. It is believed that the last step in the process is carbon monoxide (a poisonous gas) to carbon dioxide. This is also the slowest step by far and when combustion conditions deteriorate some upstream bottle necking occurs in the chain of combustion reactions. This results (according to some authorities) in polymerization of smaller partly burnt molecules into much larger ones, which become visible as soot, or black smoke.



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BLUE smoke ..

Blue smoke is caused by engine lubricating oil burning. The oil can enter the combustion chamber from several sources including ..

Worn valve guides, or seals
Cylinder &/or piston ring wear
Cylinder glaze
Piston ring sticking
Incorrect grade of oil .. too thin and getting past rings, or valves guides
Fuel dilution of the oil, making it too thin.
Blue smoke is often evident at cold start, which can reflect reduced oil control due to carbon fouling deposits around the piston rings and/or cylinder glaze (which is actually carbon deposited in the machined cylinder crosshatching. These tiny grooves actually hold a film of oil, which in turn completes the seal between the combustion chamber and the oil wetted crankcase).

Blue smoke should not be evident at any stage.

An engine may burn oil without the evidence of blue smoke, because good compression burns oil quite cleanly, however, it is not acceptable for any new engine, or engine in good internal condition to burn large amounts of lubricating oil.

Once again, restore physical cleanliness to all components. Replace worn parts where necessary. In some situations, where the engines are pretty worn, but you just need to keep them in service, cleaning with the previously mentioned products, followed by effective additional anti-wear protection, will reduce internal stresses on all those tired components, providing extended service life. Our SupaSLIP achieves this for many of our customers



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is helpful information is found at http://www.neptuneproducts.co.nz
Article detailsArticle ID: 60Category: KnowledgebaseDate added: 2011-03-21 09:55:55Views: 476
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[Steve Dion]

Dean: I would r/r the exhaust hose to see if there is an issue there.

I also think that your engine SHOULD NOT rev that high in neutral (I may be wrong) but that is what the govenor is supposed to prevent. This will not damage then engine but I don't think you want it reving that high for any prolonged period.

I would also check our your tach and be sure that it is reasonably close. There have been many posts about Yanmar tach's so just be aware.

Once you get that hose checked and if you don't find anything, maybe a NEW Yanmar mechanic would be in order.

Does you boat have a built in muffler (like our '85 Hunter 31' had) or is it a replacable one?

 

[Dean Strong]

Thanks for the great ideas. I'm going to keep at it until this thing runs clean.

Tomorrow I'm going to replace the vented loop on the raw water line leading into the mixing elbow. A poster from Australia mentioned this on another site. It is clogged, and probably restricted raw water flow, but not enough to affect engine temp significantly. Just another variable to eliminate.

I'm also going to investigate the thermostat, and if its not too hard (and costly) pull and possibly replace it. It may be that the engine is not reaching operating temperature and the injectors are not seating correctly at cruising speeds.

I'm also going to inspect the exhaust hose and muffler. I haven't gone there before, so I don't know how hard it will be to detach and inspect; possibly replace the muffler.

I've contacted a new Yanmar mechanic, and am scheduling a service call to have him check out the no load idle issue and test the exhaust backpressure. I have no clue how this is done, but it seems like the best next step.

I'll keep posting.

 

[Steve Dion]

Dean:

You may want to make a visual inspection of the actual hose. "If" it cracked/checked you may just want to replace it NOW. This is not a simple job on my prior H'31, so have some assistance if you decide to change it out.

 

[robertsapp]

You might want to cross-post your question to the Engines forum. Lots of Yanmar owners out there who don't sail Hunters.

 

[Dean Strong]

Yes, I posted on the Engines forum.

Another clue: "inspect the thermostat after every 500 hours of operation. . . always inspect when white smoke is emitted for a long period of time after the engine starts . . . replace when it has been in use for a year, or after 2000 hours." Yanmar Service Manual, pg 8-15.