# Calling all Yanmar experts. Black dusty soot out of exhaust from a Yanmar 3gm30



## Jim M Miranda

Black dusty soot that floats on the water coming from a yanmar 3gm 30. We've done everything from the basics replace injectors check fuel replace air filter check compression we even adjusted the timing in the problem persists. She starts up right away but when we rough up hard she dumps soot into the water. When tested the boat on the hard and bypassed all the exhaust system and the problem persists so we know it's not a load issue from the prop. 
, since the engine runs well other than that I'm considering another option period connecting a hose to the exhaust and some sort of a filter to collect the black soot so I don't leave a trail in the water.


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## Minnewaska

It's unburned fuel. Backpressure is the most common reason, but injectors, fuel pumps or mixture can do it too. Any obstruction or modification to the exhaust system? Too many bends or too small a diameter can do it. Is the mixing elbow corroded?


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## MarkofSeaLife

Jim M Miranda said:


> when we rough up hard...


As English is my first language I don't know what this means. 
My guess it's something about revs...?

The Yanmar handbook says this problem can be solved from 3 very short full throttle bursts. Or a run at Wide Open Throttle.

But if you have already done all the things you've said you probably had a mechanic give you advice?

It's way beyond me.


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## BillMoran

This sounds suspiciously like the "blue smoke" problem that happens with older cars. I had an old Toyota a few years ago that would do this when you put the pedal to the floor. A mechanic told me that it's basically a symptom of a well-used engine. They way I understand it, if an engine gets a lot of use but it properly maintained, everything wears out equally. As a result, the engine still runs well, but when under load it will burn a little oil or otherwise run less efficiently than when new.

Since diesels tend to generate soot when things aren't perfect, I'm guessing that the soot under load (that's what you mean, right?) is a similar symptom.

I'm not a diesel mechanic, though. This is just a guess. At this point, you'll probably need to pay a diesel mechanic to go over the engine, probably have to do a compression test, etc. to be sure.

I did have one surveyor offer some advice that might be helpful: While the engine is running, pull the dipstick. If oil tends to squirt out of the dipstick tube, it generally means the pistons are worn and compression/firing pressure is leaking into the crankcase. If the engine runs fine otherwise, it's generally a sign that it's just old. It's a good sign that it's time to start budgeting for a rebuild or new engine, as the problem is just going to keep getting worse, and the engine power will be low, as well as fuel consumption will be high.

Hope this is actually helpful.


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## JimsCAL

Soot is definitely unburned fuel. Don't consider a filter in the exhaust. You need to find the problem, not put a bandaid on it that will only cause more. Sounds like you've done all the common ones. I guess you need to find a good mechanic.


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## capecodda

OK, this is a guess, but here goes.

I'm guessing that it ran poorly, you then replaced injectors, retimed, etc. Reading between the lines it's running well now, low smoke, nice sound, good power, but some dried up carbon in the exhaust?

Is it possible that there is plenty of crud in the exhaust system remaining from when it ran poorly? How long since you did all this tuning and how much run time? Wondering if it's running well now if you ran it hard for a few hours does it still emit carbon?

Lots of guesses here, could be all wet. Good luck.


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## Jim M Miranda

2 mechanics as a matter of fact, definitely not compression and load doesn't make sense because this problem happens even when we tested it out of the water and had bypassed the entire exhaust system (throttling up in neutral still dumped soot but if we do it gradually, the soot is reduced significantly). I also forgot to mention that it is a rebuild from about 2 years ago.


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## Faster

Has the exhaust elbow been checked/cleaned/replaced?

Could be an accumulation of carbon now being 'blown out' with the flow/pressure of high revs?

FWIW I have had a 'rebuilt' injector that needed immediate replacement.


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## Capt Len

Pre combustion chamber bits out of position or the insulating washers at the injector tip missing or doubled. Just head scratching here.


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## overbored

Were the injectors rebuilt or new? I have seen several rebuilt injectors that were not done correctly cause this problem


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## Wes

Hope this helps...

Smoke Colors

There are three basic types of smoke, as identifiable by their colour. And then there is blowby smoke (or just blowby).

BLACK SMOKE is the most common smoke emitted from diesel engines. It indicates poor and incomplete combustion of the diesel fuel. There are many causes, including

Incorrect timing
Dirty or worn injectors
Injectors sticking open too long (Common Rail Diesel type)
Over-fuelling
Faulty turbocharger (ie not enough air to match the fuel)
Incorrect valve clearance
Incorrect air/fuel ratio
Low cylinder compression (eg sticking piston rings or worn components)
Dirty air cleaner
Restricted induction system (eg system too small or kinked inlet piping)
Carboned up intake manifolds (esp Common Rail Diesels)
Other engine tune factors
Poor quality fuel
Excessive carbon build up in combustion and exhaust spaces
Cool operating temperatures


BLUE SMOKE is an indication of oil being burnt. The oil can enter the combustion chamber for several reasons.

*Worn valve guides or seals
*Wear in power assemblies (ie cylinders, piston rings, ring grooves)
*Cylinder glaze
* Piston ring sticking
* Faulty turbocharger seals
* Incorrect grade of oil (eg oil too thin, and migrating past the rings)
* Fuel dilution in the oil (oil thinned out with diesel)

WHITE SMOKE occurs when raw diesel comes through the exhaust completely intact and unburned. Some causes of this include

Faulty or damaged injectors
Incorrect injection timing (could be a worn timing gear or damaged crankshaft keyway).
Low cylinder compression (eg caused by leaking or broken valves, piston ring sticking, cylinder and/or ring wear, or cylinder glaze)
When white smoke occurs at cold start, and then disappears as the engine warms up, the most common causes are fouling deposits around piston rings and/or cylinder glazing.


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## Faster

White smoke could also be burning coolant on an FWC engine (head gasket issues) - fortunately not the OP's issue.


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## midwesterner

DISCLAIMER: I have no experience with diesels.

One of my first thoughts was contaminated fuel. The OP said that he has run a compression check and replaced all fuel system and combustion components and that the black soot is emitted even when the exhaust system is bypassed.The engine has had a recent rebuild. 

About the only thing left would be contaminated fuel, I would think.

What happens to diesel fuel when it gets that microbial growth in it. I know that you can put the anti-microbial treatment in, but if it was heavily contaminated, what happens to the dead microbes when they are burned in the engine?

Did the tank sit for a long time with less than a full tank of fuel while the engine was being rebuilt?


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## MarkofSeaLife

It seems you have done everything a cruiser does perfectly: everything except what the instruction book says.
Of course I never read the Book either so I don't know that the photo below is on Page 27 of the Yanmar book. Nor did I actually read the excerpt to see that it's a pretty close fit to your symptoms and bypassing the exhaust will not have an effect. 

A friend of mine recently did not do what the book suggested (a different problem) and in frustration bought a brand new engine! 
I shook my head in disbelief as he badgered me to support his $20,000 (incl installation) proposal. No, he said, I was wrong, he neeeeeded to spend the money. 
Great guy. The Yanmar dealership loves him.


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## Minnewaska

Jim M Miranda said:


> ....load doesn't make sense because this problem happens even when we tested it out of the water...


When you increase throttle on a diesel, there is always load. Not as much out of water, but you're pushing more fuel into a cylinder that isn't running fast enough to burn it yet. Fuel systems try to compensate for this.

Load creates backpressure, which keeps the cylinder from speed up fast enough to burn the additional fuel. When you throttle up slowly, you don't see as much soot, because you're giving the cylinder more time to catch up.

Even on the hard, you must have been running cooling water. When you say you bypassed the exhaust, what does that mean? Was exhaust and cooling water still mixing in the elbow? That is a very common place for corrosion, which also creates backpressure. Elbow lifespans are limited.



> I also forgot to mention that it is a rebuild from about 2 years ago.


This is the yellow flag for me. There is absolutely no standard for what that means. All sorts of worn stuff could have been reused.


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## RichH

A diesel engine _absolutely_ needs two things to combust fuel correctly: 
1. proper combustion chamber _temperature_ and 
2. proper combustion chamber pressure (the combustion pressure is dependent on combustion chamber temperature). 
The 'DIESEL Cycle' for ignition of fuel in a diesel engine is totally dependent on *both* (simultaneous) correct operating temperature AND pressure in the combustion chamber for complete fuel 'burn'. In a diesel engine, combustion _pressure_ is interdependent of combustion _temperature_ .... you must have both at normal values for 'full' combustion. 
Note - IF you're ambient inlet raw water temperature is still COLD there's a good possibility that the cold engine inlet raw water temperature is *too cold* for a relatively 'fast' engine warm-up to proper engine operating temperature ... the engine will have difficulty in bringing its combustion chamber temperature up to that 180° operating temperature; and consequently, the combustion PRESSURE will be insufficient; hence, unburned fuel (& soot) coming out the exhaust. If you 'gun' a cold diesel engine, you'll usually always get soot in the discharge water.

Rx: first evaluation is to slowly bring the engine up to normal operating temperature before doing any cursory evaluation for 'soot'. If after reaching that ~180° normal engine temperature ... and you still get 'soot', THEN ........

Suggest you further evaluate the following:
• Evaluate the engine for correct operating temperature. This is especially important in locations where the ambient water temperature is COLD (much less than ~*80°F* - the normal 'design' inlet raw water temperature). 
Start the engine and with the prop/transmission engaged _slowly_ increase the engine rpm until the inlet of the fresh water circuit to the heat exchanger reaches ~170-180°F. 
If you increase engine rpm BEFORE the engine comes up to correct operating temperature (thus also at less than correct operating PRESSURE) you will usually alway get soot inside the exhaust system and coming out of the exhaust into the water, etc. If significantly less than 180°F then, then correct the problem by cleaning (acid soaking) or replacing the thermostat, etc. 
Note: all COLD diesel engines will issue 'soot' out the exhaust when at LESS THAN normal operating temperature, especially when run at near 'full' rpm.

• Do compression check for leaking valves and worn piston rings. Do this on an engine AT or near (as close as possible to) operating temperature (180°F). When doing this evaluation open the valve cover and inspect to SEE that the exhaust valve stems are moving at 'full stroke' of the valve stems, as a 'sticky' exhaust value stem will 'release' combustion pressure. If there is any 'suggestion' of a sticking exhaust valve stem, soak the probable sticking valve stem with penetrating oil & manually 'work' the valve stem up and down to 'free' it, then repeat the compression test to validate any changes in pressure.

• If the engine 'does' come up to full 180° operating temperature (when running at near full load at near full 'cruising rpm'; and, the compression pressure values were found to be 'near' correct; ......... and, you're still getting noticeable black smoke and soot .... THEN, remove the fuel injectors AND high pressure injection pump and send them to an 'fuel injector shop' for evaluation for rebuild or replacement. (every large town in North America should have a fuel 'injector shop'.) 
IF after validation of the injector pump and injectors, you still get 'soot' and a bit of black smoke out the exhaust when the engine is running at near 'full load', then consider to have the prop pitch to be evaluated, as a 'lugging' engine (because the prop isn't allowing the engine to be 'turning' as fast as necessary and the fuel system is 'over-fueling' the engine ... due to incorrect pitch (blade angle) on the prop.

Rx: dont 'gun' a cold diesel engine; or, you're going to fill (can also 'block') the exhaust system with 'soot'. Only run at near full rpm when a diesel engine is nearly at its 180° design operating temperature. Don't do this and you will eventually block your exhaust system and usually with great deposition of soot at the 'water injection elbow' near your water lift muffler.


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## Bleemus

Go run at full load for thirty minutes and report back please. Diesels that spend too much time without load i.e. charging batteries do this and you just need to load it for time to clear it up. Grab that throttle and dont be shy!


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## donsboat

Exhaust elbow, Exhaust elbow, Exhaust elbow. Yanmar 3gm exhaust elbows will clog up with low rpm use and over time anyway. As well as the salt and carbon deposits building up they actualy corrode from the inside out to the extent that they can become paper thin and fail, resulting in engine failure and a bilge full of black carbony water. Their life is a safe 2 years and after that you're gambling. This sounds so typical of a blocked elbow, but don't take my word for it, ask a reputable Yanmar dealer and I'm betting he'll tell you the same thing.


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## gamayun

Yeah, this is where my money is at, too. If it bogs down as you try to increase RPM and it spits out black soot, I'd pull the elbow and take a look inside. It's simple (remember KISS) and doesn't cost anything to check other than maybe the purchase of some large wrenches. Mind the gasket though, if you remove the whole assembly from the bolts directly off the engine. I found out the hard way that it's hard to see the gasket slip when you're reinstalling everything.


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