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Tspringer 01-22-2010 08:02 AM

Yanmar baffling black smoke
I purchased this boat, a 1981 Stevens 47, in March of 2008. It has a Yanmar 4JH2-HTE 75hp turbo/intercooled diesel engine that was installed in 1992. At the time of my purchase the engine had approximately 3500 hours. It now has about 4000 hours. It has always run great for me. It has always put out a small amount of light grey smoke at idle and under load but not anything excessive, barely noticable really. It also would put out some black smoke running at maximum rpm driving the boat at hull speed. It has never burned any oil, I do not have to add any oil between oil changes. The engine has always started very easy, on the 3d or 4th turn over when cold.

I brought the boat from St. Thomas to Jacksonville FL in June of 2009 to do extensive refit work. Since June of 2009 she has been in a slip not being run until Monday of this week with the exception of 10 minutes running to and 10 minutes from being hauled out in mid December 2009.

During November of 2009 I removed a number of ancilliaries from the engine to facilitate cleaning and painting everything. I removed the air cleaner, turbo, after-cooler, turbo oil drain tube, alternator and injection hard lines to the injectors. I stripped the engine area, treated all surfaces, primed and painted everything. The turbo was cleaned out with carb cleaner and compressed air but not at high pressure and it was not spooled up to any speed without lubrication. When reassembled, and now as verified today by hand and direct observation the turbo spins freely. Everything was reassembled and after some problems related to figuring out how to bleed the injectors so the engine would run (the Yanmar manual did not give the correct procedure) it fired right up and ran well. I did not run it under load at that point but it fired and ran normally.

When we left the slip on Monday of this week to head out cruising, the boat threw large amounts of black smoke and the exhaust water was black with soot. This was at both low rpm and under load. At cruising speed of 2400rpm the smoke and the exhaust water were very sooty black. After 3 hours of running the transom well stained with black soot.

We anchored out and I began investigating. It appeared that the oil level was higher than when we left (it was right at the full mark and after our run it was 1/2" - 1/2" above the full mark) and the oil seemed to be diluted. It did not reak of diesel, but its viscosity between your fingers did not feel like non-diluted oil. So I feel it was leaking fuel into the oil thus raising the oil level.

I called the local Yanmar dealer and make arrangments to take the boat to them Tuesday morning. I changed the oil and we motored up there early Tuesday, a run of less than 30 minutes. The engine started normally and ran fine but of course smoked like crazy.

The Yanmar dealer diagnosed a likely injector issue. They pulled the injectors and indeed they looked pretty bad. The injectors were sent out to an injector shop. They reported that 1 was all but totally plugged up, 2 others were pretty bad and only one was "decent". I had a set of new nozzles (brand new in sealed new containers) and these were used to rebuild the injectors. So we have new injectors (with new nozzles the injectors are new). At this same time based on advice received online I replaced the fuel lift pump with a new unit I had onboard. I disassembled the old fuel lift pump but did not find any obvious cracks or issues with the internal diaphragm though it was clearly old.

We ran the engine with the new injectors, new oil and filter, new fuel lift pump, new fuel filters and clean fuel..... and while the engine did idle better and it general seemed to run smoother it still threw the black smoke.

We conducted a sea trial with the mechanics on board. The maximum rpm the engine will make is 2,950 measured with a seperate tach tester and matching my onboard tach, at full throttle. Thats all she will give and at that rpm under full load she basically pours black smoke and the exhaust water is sooty black.

We tested the turbo boost and at max rpm it is about 9psi. It should be around 15psi at max of 3700rpm at full throttle. The turbo is spinning but the engine appears to be overloaded and cannot reach full rpm..... or at least that is the conclusion the techs are at right now.

We removed the valve cover checked for any obvious valve issue and turned the engine over to listen for any obvious top end leaks. The engine clearly has compression as TDC can be felt as it approaches and there is no leaking apparent or other noises. Also, even when cold the engine now starts on the first turn... it basically spins and starts immediatly. Compression certainly seems good. When running we removed the breather line and there is no pulsing or any sign of any blow-by indicated at all.

We removed the after-cooler and checked for any blockage of the intake air charge. There is none, it was relatively clean. There is no blockage in the air cleaner assembly and we ran the engine with the air cleaner off with no change in the problem. With the air cleaner off the turbo can be easily spun with the finger and no obstructions or sticking is noted. Additionally when the engine is run the turbo can clearly be heard though the techs say it is not as loud as it should be because the engine is not building the rpm and boost at load as it should (overloaded).

The engine will rev to 4,000 rpm at the dock not under load (out of gear).

The techs and the Yanmar service rep at Mastry all seem to think that issues with the fuel injection pump are pretty much impossible and that any adjustments that would effect this are not possible at the injection pump.

Checking the oil after the sea trial and running for test it is not possible to tell for sure if the engine is putting any fuel in the oil. The oil level before running seemed to be just a tiny bit over full, I just checked the oil and measured the level exactly and the oil level is 7/8" over the full mark.... but the oil does not smell like diesel and it does not feel diluted (though thats not all that easy to tell).

Perhaps when I checked the oil before not all of the new oil had found its way to the crankcase? Would being overfilled perhaps cause the cranshaft to actually spin in oil and thus overload the engine preventing it from reaching max rpm? Would this be possible with no indications of oil being throw about in the breather or such?

Can a Max-Prop magically change its pitch all by itself resulting in the engine suddenly being overloaded when before it was fine? Could some piece of trash like a plastic bag be wrapped around the max prop in a fashion such that the spurs would not cut it off but it would overload the engine while also not causing any abnormal vibration nor give any other sign?

Engine run testing and sea trial were conducted with engine space doors removed on 3 sides... she is getting all the air any engine could ever want.

Are there in fact aliens living in my bilge screwing with me intent on destroying my cruising dreams and bank account?

Baffled in Jacksonville....


sailingdog 01-22-2010 08:41 AM

Black smoke is often caused by two things: First, too much fuel getting into the engine cylinders... second, running under too high a load—often caused by a fouled prop.

Since you've replaced the injectors and such, I am guessing the issue is a load-related one, not a fuel related one. Have you checked to see that the prop shaft is clear of any line wraps and that the prop itself is clean?

Also, you said you were using a Max prop, which is a self-feathering prop. Yes, self-feathering props can change pitch—that's kind of the definition of a self-feathering prop... and if they're not properly maintained, can cause this kind of problem by not working properly.

If something is wrapped around the prop shaft or prop or jammed in the max-prop's feathering mechanism, it doesn't necessarily have to cause vibration of any sort. Diving on it or hauling the boat and doing a visual inspection is the only way to tell.

klem 01-22-2010 09:11 AM

It sounds to me like there might have been 2 issues going on. Issue 1 that you mention is the raising oil level and fuel dilution. This is commonly either an injector problem or a lift pump problem, both of which you have changed. You also mention that you couldn't detect dilution after your test run which seems hopeful that you have solved it. Remember, the oil level will go up a little after a hard run but it will go back down again as the engine cools off.

Issue 2 that you mention is the exhaust color. The gray color that you used to see likely means inefficient combustion due to plugged injector nozzles which you have now had replaced. The black smoke is caused by your air to fuel ratio being off. The two possibilities are that you are injecting too much fuel or that you are not pushing enough air. On that engine, to inject too much fuel, you need to be lugging it which means putting on too great of a load so that it cannot get up to rpm. The possible problems include a fouled bottom, prop, or shaft or an overpitched propeller. It will be easy for you to check for fouling and harder to check the prop but it is pretty unlikely that the prop pitch magically changed but not completely out of the question. The other thing that can happen is that the cylinders are not injecting equal amounts of fuel and one cylinder will overfuel while the others basically don't do any work but you would be able to hear this.

The other option which is a good place to start working if you bottom is clean is that you are not getting the air you need. It sounds like you have inspected the turbo and that it appears to spin freely and has no missing fins. The next place to look would be boost leaks. These can occur on either the exhaust or intake side however, you would probably have noticed an exhaust one if you were running with the engine room open. I would check all the sealing surfaces between your turbo and intake. Since you are only seeing 9psi, I suspect that you have a boost leak. It does not take a very large boost leak to cause problems, this is extremely common in diesel pickup trucks. The first thing to do would be to inspect all of the rubber boots and seals for chafe. If they are fine, it is likely a sealing problem. Some people prefer to take all of the boots off and reseat them and others prefer to use a mist bottle with very soapy water to look for leaks with the engine running. Chances are if you find a leak and reseat it, your problems will go away. The performance diesel pickup truck guys have come up with some interesting solutions for people who have trouble getting a good seal.

Good luck.

jrd22 01-22-2010 06:57 PM

It sounds like the engine is blowing black smoke both in neutral and under load, is that correct? You need to have an oil analysis done so you can confirm whether you are getting diesel in the lube oil, could point you in the direction of the problem. A turbo shop should be able to bench test the turbo to determine if it's performing properly off the engine (developing proper boost). Klem might have something there about a leak on the intake side, especially since all that stuff was r/r'd for paint.

sailor50 01-22-2010 07:22 PM

2010 minus 1981, what shape are the fuel tanks in?

bljones 01-22-2010 08:19 PM

If the engine sat idle for almost seven months, and having swapped out all of the usual likely suspects, and if she revs to 4k with no load, then I would look at the prop - I bet your prop is fouled, loading up the engine, which explains your symptoms.
Too bad your marine mechanic didn't suggest a dive on the prop BEFORE spending time sea-trialing the engine, because that would either solve the mystery, or eliminate one more suspect, leaving us only to conclude that yes, aliens are responsible.

either that, or those meddling kids and their dog.

timebandit 01-22-2010 10:39 PM

Clean the prop.

"I brought the boat from St. Thomas to Jacksonville FL in June of 2009 to do extensive refit work. Since June of 2009 she has been in a slip not being run until Monday of this week with the exception of 10 minutes running to and 10 minutes from being hauled out in mid December 2009."

sigmasailor 01-24-2010 04:54 AM

I think you need a new or overhauled turbo. Obviously the turbo is not delivering the required air to burn the fuel that is squirted into your cylinders; that is why you get black smoke.

I was trained as a marine engineer and overhauled my share of turbo's. We used to take them apart, soak them (housing and turbine wheels including shaft but not the bearings) in carbon solvent (would be a no no in these days) and reinstall them with new bearings (which came ultra clean in sealed cans supplied by Brown Boveri) and seals. After that they would be OK for the next 10.000 hours. I am talking about turbo's with diameters of 1 up to 6 feet for the real marine engines here. The turbo's on Yanmar diesels are a lot smaller, rotate really fast (100 - 200 k rpm) and have super sensitive bearings and seals. My guess is the carb cleaner or foreign matter ruined the bearings.

Good luck with your troubles; I really understand your frustration.


gathhill 01-24-2010 10:32 AM

stabbing in the dark?
Is it possible your water intake for the engine could be clogged or obstructed? Just a thought and not being any sort of an expert I would blow it out anyway. Could be some growth or ? up there restricting cooling and causing who knows what. In the end it will be something obvious.

Shortman 01-24-2010 12:42 PM

Also if checking raw water intake, check line before strainer. This past summer I had eel grass clogging the intake before the strainer as it had caught on the lip of the hose elbow. Over heating smoke was white/gray not black. Also my engine & therefore inlet hose is smaller (3/4") than yours is likely to be.

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