Yanmar - black smoke in exhaust

[JSL3]

Calling all diesel experts...

I'm not very knowlegable about diesel engines but I have read a number of posts on 'black smoke' so far on this site and others.




I have read the basic symptoms from a number of sites but http://www.catalina320.com captured it quite well:

Black Smoke is caused by partially burned fuel. When the fuel/air mixture increases there is insufficient oxygen present in the cylinders to complete the combustion process. Large quantities of carbon are then produced which appear from the exhaust as minute black soot particles. Engines with turbochargers have additional sources of black smoke.

Black Smoke Insufficient Air:

Causes: Air intake filter clogged [2] - Air intake restricted [3] - Exhaust restricted [3] - Leaking inlet or exhaust valves [4] - Poor engine room ventilation [4]

Black Smoke Excessive Fuel:

Causes: Defective injector(s) [1] - Incorrect injector nozzle [3] - Injector pump incorrectly set [4] - Low fuel grade [4]

Black Smoke Engine Overload: As load increases the governor senses the slight decrease in RPM and adjusts the injector pump to deliver more fuel. If the engine becomes overloaded then the increase in fuel does not increase RPM and no extra air is being sucked into the cylinders. Net result - soot:

Causes: Boat bottom dirty [1] - Propeller dirty/fouled [1] - Engine alignment incorrect [2] - Propeller incorrect [3] - Transmission incorrect ratio [3]

So here are my specifics:
1986 Pearson 28-2 which I've owned for 2 years. No problems thus far.
Yanmar 2GM20F, original engine, unknown hours, ran well until today
Last fuel filter change in fall before hauling for winter

Symptoms today:
Max RPM I could achive under load was 2700 (that would only drive the boat at aprox 4.5 knots), normal max rpm under load is over 3100 rpm (which will normally drive the boat at just over 6 knots)
At 2700 RPM thick black smoke would come out of the exhaust, if I backed down to 2500 RPM smoke went away and speed woud drop to 4 knots or so
Plenty of water in the exhaust
Back in the slip, in neutral I could max the RPMs out at 3400 or even higher with no black smoke

Other info:
Not had this problem before and there has been no change to prop or other engine components.
I can't imagine the bottom or prop are fouled since it was cleaned, scraped and painted just before launch on April 15th or so of this year.

I'll be having a mechanic take a look at it but was wondering what troubleshooting steps and/or questions to ask the mechanic that some of you might suggest.

Anything jump out at you?


Thanks in advance.

[Omatako]

The end of your inserted article probably holds the clue - I reckon your prop has something wrapped around it. That would account for the lower than normal RPM, the lack of smoke when revving free, the rapid fall-off in speed at a lower RPM as well of course as the black smoke.

[JSL3]

Thanks Omatako.
I will check that. Also, you undersood correctly that there is no smoke revving free. I should have included that. I'll fix it in the orginal post.

Originally Posted by JSL3

Symptoms today:
Max RPM I could achive under load was 2700 (that would only drive the boat at aprox 4.5 knots), normal max rpm under load is over 3100 rpm (which will normally drive the boat at just over 6 knots)
At 2700 RPM thick black smoke would come out of the exhaust, if I backed down to 2500 RPM smoke went away and speed woud drop to 4 knots or so
Plenty of water in the exhaust
Back in the slip, in neutral I could max the RPMs out at 3400 or even higher with no black smoke.

[Northeaster]

Have you been using the boat regularly since launch in April??

When was the last time you had it out, and engine ran well?

If it has been a month or so, you may have enough growth on the hull and prop to account for this??

[bubb2]

Count your dock lines or your neighbors dock lines, or you got a crab trap you been dragging around, this sounds like the classic fouled prop!

[davebkanelavie]

Checking for a fouled prop would be easiest thing to check first. A surprisingly small amount of growth can have a profound effect on performance.

Let us know how it goes.

[JSL3]

Problem Solved.

Thanks to all who posted (Omatako, Northeaster, Bubb2, Davekanelavie), you were right on! Barnacles!

Although it will cost me the price of a quick haul and scrape, I'm very happy to find it was nothing serious. As I stated, its only been in the water for 10 weeks. My marina guy told me they coat the prop/shaft with a spray on anti-fouling agent but didn't know the name of the product. He also said this year has been a bad year for barnacles in my area, he's had to haul quite a few boats. I'm going to have to try somehthing new next year and I'll have to try to use the boat more so those critters won't be able to hang on as well.

Here's what I found this morning.



Those critters must get dizzy!



The bottom paint didn't look bad at all. Was redone this winter.


I told my wife, we'll just have to use the boat every weekend. It will be cheaper to try to keep the barnacles off a spinning prop than to have to have it hauled now and then.

[bubb2]

You do need to get out more!

[L124C]

Yikes, thats not a drive train, it's a reef Poor little Yanmar! I've sometimes noticed that my motor (same one) will smoke at 3000 RPM if I'm fighting a strong tide and/or headwinds. If I back off the RPM, it seems fine. The motor purrs at 3000 otherwise, so I assume it's not a prop issue. This has never made sense to me, as the motor shouldn't "know" what the opposing forces are. Right? They should simply make the boat go slower. Or, are the forces somehow "lugging" the motor? Hypothetically, if the boat was tied to the dock, shouldn't the motor turn effectively at 3000 RPM? Dock, line, boat and dock cleat failure aside of course Someone please explain

[Gary M]

I found a web site with the mainteance manual, mine is on the boat. It lists monitoring the exhaust colour and if it is black is says you are overloading the engine and this should be avoided as it will shorten engine life.

Diesels like to be worked but within limits. It also says if you are running for long periods of time at slower RPMs that every 2 hours you should rev the engine up several times to clear it out.

Web site can be found here
Yanmar Manual

Gary