This Can't Be Good.... Black Smoke & Soot

[markpj23]

My Yanmar 4JH2-DTE with 'only' 4,650 hours on the meter is now leaving a black substance on the water behind the boat. Looks like soot to me as it does not break into a sheen like I'd expect with fuel or motor oil being discharged out the exhaust. Have noticed that this time out the engine does not seem as powerful as before.

I also ran hot when above 1900 RPMs - something that usually did not happen unless I ran it hard above 2,300 RPMs or so. Water ouput seems normal.

I've been told that the exhaust mixing elbow near the turbocharger gets clogged with carbon quite frequently on these model engines. My other thoughts are that I may have a leaking injector. The engine fires right up normally but it's not making full power as I said before. Black smoke usually means insufficient air in combustion to me... and the other side of that equation is too much fuel.

Any ideas on what I should check first?

[Richhh]

Several things can cause your symptoms:
1. injectors need servicing.
2. Lugging the engine --- high load at not high rpm. (Pitch too great on prop.)
3. Clogged water injection nozzle - creating high back pressure ... when you disassemble add a 'gage boss' to the manifold line so you can periodically measure the back pressure .... dont leave the gage installed but put in a bronze pipe plug into the gage port as exhaust gases will 'kill' a gage in very short order. Two things can clog the water injection nozzle: carbonates that precipitate out of the hot sea water and "coke" from incomplete fuel combustion.
4. bad fuel (decomposed / old fuel) .... the heavier fractions of old fuel wont combust very well but will deposit as 'coke' in the exhaust manifold.

Since you are not 'making full power', the first place to look is probably the water injection nozzle (high back pressure in the exhaust manifold).

hope this helps.

[Alan Wheeler]

Richhh, I don't quite get the block water nozzle creating high back pressure. Can you explain??

Mark, your right with your two possible causes of black smoke. Always start with the simple elements first. Firstly, is your aircleaner clean and dry?? and is there are a good supply of air to it's intake??
Next, how long ago since your hull and prop was cleaned? Are you reaching normal cruising speeds at normal RPM?
If yes to 1 and 2, go to 3.
Exhaust after a turbo can indeed cause issues. I would remove the pipe and inspect. Is your turbo operating correctly as well. You do not want to be hearing high pitch wistles from them as they spin up. Ensure dump gate mechanism is operating and not siezed.
I won't go further just now, till you answer some of those questions, or this all just gets too complicated and confusing.

[Richhh]

Heat sea water to above ~145°F/63°C and the carbonates in solution will drop out and form insoluables (rocks) on the walls of the exhaust header in the area of the injection port. If the carbonates build up to a degree that constrict the total gas/water flow you will have back pressure. Most times as the carbonates are converted to insoluables, they simply get swept through by the flow ... but sometimes/rarely they can form downstream of the water nozzle and cause blockage there.

(Normally) the same precipitation will/can happen in the cooling water circuit / exhaust header but there will only form a blockage of the water circuit anytime seawater goes over ~145°F. It all depends on the location of where the carbonates are precipitating/forming. Like I said, its a rare occurance to have the precipitation occur AFTER the nozzle but it can happen if the water gets hot enough.

Incidentallly, it did happen on my Yanmar 3QM30 ... with the addition of 'coking' of fuel with the 'rocks' that were forming ... what a mess that caused quite high backpressure. The exaust system was/is a 'cobbled' affair made out of black iron pipe, etc.

[markpj23]

Some recent history that answers the questions:

We DID have a severe fuel contamination issue, but we replaced all fuel and then ran for some 200 hrs with no problems.

The boat hull is clean, recent bottom job and no visible scum / growth. My normal cruise is 7kts at 2200 RPM. Since I now get too hot at that engine speed, I can run about 6kts at 1900 RPM. I believe the prop, shaft and hull to be clean.

I probably have a less than perfectly clean air filter... however not ecessively dirty. Plenty of air supply to the engine. Dry filter from my quick check.

I DO - and have since we've owned the boat - have a high-pitched whistle / whine from the turbocharger. Becomes noticeable at around 1700 RPM or so, and gets louder as engine speed increases. I don't think the pitch changes much at all however - same "note" with varying volume.

Interesting to note that one of the spares kept aboard by the previous owner is an exhaust mixing elbow. Was that out of preparedness or past experiences with this engine...??

No changes to anything - except the engine oil & filter change I did just prior to underway this time out. Maybe a bit too much oil added but nothing excessive per the dipstick. That plus both me & the boat are a month older.... No other changes since the previous operation.

Thanks guys - I can't wait for steps 3 through 13.... as I'm sure they get more expensive / difficult as we go on...

[Sandero]

My guess is that you have one or all of the following:

fouled injectors causing poor spray pattern and unburnt fuel

valves which are corroded, or not seating or not in correct timing causing unburnt fuel

bad rings which are causing less compression and unburnt fuel

fouled exhaust elbo and exhaust hose lined with carbonized exhaust , Exhaust elbos last a few thousand hours and then are caput.

dirty air filter

Clean the oil with an oil treatment and do and aoil change. Then do that again to remove all the crud in the lube system and channels of the block.

Clean the air filters

Clean the exhaust elbo

Inspect the injectors and have them tested for spray pattern

send the old used oil to be tested. The report can tell you what is not working in the engine. Costs about $35

Check the fuel delivery system including pump and filters

Check the cooling sytem, hoses, strainer and pumps

inspect the valves and if the look ok and seat well, set the timing.

Make sure your fuel is OK and add some cetane and fuel stabilizer.

Jef
sv Shiva
Contest 36s

[Alan Wheeler]

With all due respect guy's, keep it simple. The fault is low revs and over heating. That is NOT caused by loss of power from a worn engine. There is another issue here and it sounds like the engine is over working.
Pat, any idea's to throw in the pot???

FWIW my vote is for 1 or more bad injectors, and/or plugged exhaust. If the injectors have allot of hours on them, just rebuild or replace them and get that out of the way. Then, if the problem doesn't go away, start disassembling the exhaust.

[never monday]

I'm thinking....I'm thinking....

You said something about a whine from the turbo. Thete should always be a wistle from a turbo. Has this gotten excessivly louder?
What part of the Soutwest are you in? I'm driving to Huntington Beach Ca next week and could stop if it's not far out of the path.

[markpj23]

Pat - perhaps whistle is the more correct term to use. Not a whine that varies in pitch like from a jet engine but more of a steady pitch whistle that increases in volume as the RPMs go up.

I appreciate the offer to stop by, but Tucson is way out of your way - plus the boat is in Texas. (Where we hope to be soon)

[Alan Wheeler]

Whistle is what we are talking about. There will always be "some" noise, but as long as it's not too loud and certainly if it seems to be louder than you have been used to, it could be a problem.
It won't change pitch, just get louder. It can be caused by several factors from carbon build up , chip on a blade to a worn out Turbo. The important factor is, these things spin at some scary speeds and you need it working just right. If it crashes, it's can be expensive. Where as if it is a clean and new bearing kit now, it could save lots of dollars.
By the way, a worn turbo bearing and seals can allow oil to pass into the exhaust and also back into the intake. If the engine is using Oil, this could be a sign as well as oil in the intake manifold. If you wipe your finger on teh inside of the exhaust outlet and it is very oily, this could be raw oil being blown into the exhaust.
I seriously would take up Pats offer to take a look.

[never monday]

A few more questons please...
When the soot started was it "all of a sudden"?
DOes it smoke and soot at all rpm?
or just when the turbo starts to whistle?
At what RPM is the smoke the worst?
Texas isn't that far out of the way, especialy if I go there first...
no seriously I was planing on goig over 40 but can drop to 10 or 20. I'm near Atlant so I can go everywhere.

[CaptainK]

And I say it's 1 of 2 things.

#1. Fuel injectors clogging up.
#2. Turbo's bearings and seals are worn out.

[markpj23]

Pat - in response to your questions:

When the soot started was it "all of a sudden"?
- No. I do remember seeing some black stuff in the wake prior to this. However I believe it has gotten worse. It's now immediately noticeable as we leave the slip. So much so that the wife spotted it right away... and she had not noticed it before as I had.

DOes it smoke and soot at all rpm?
or just when the turbo starts to whistle?
- At all RPM we have black smoke, not the 'blue' exhaust I expect to see from a healthy unit. The soot is also fairly constant... for example motoring out the channel at a constant RPM we see it in the wake. Also see it when we increase throttle, as in backing down to stop the boat. I do not think we get soot at idle

At what RPM is the smoke the worst?
- seems fairly consistent across all RPMs. By this I mean the exhaust color is the same (black). Obviously more exhaust at higher RPMs but no color difference that I can tell. Black smoke at idle, more black smoke at higher RPMs.

[never monday]

Take the time and put the spare elbow on for now, rule it out. I'm thinking it's getting atherosclerotic. This will increase the overheating by restricting the water flow speed thru the coolers. It will also increase the black smoke because you're holding in the exhaust you're trying to get out.