Yanmar 3YM20 problem

[Lathe]

Hoping somebody may have some answers/suggestions to problem I have just started experiencing with my 2006 Yanmar 3YM20 (300hrs)

Engine has just started blowing black sooty smoke at 2400 revs. Will not rev out past 2800 revs in forward gear. Thought at first this may have been due to a fouled prop, so hauled boat to check and clean. No fouling present.

Engine will rev out in neutral to max revs (with a little puff of dark smoke for an instant before clearing at 3200 revs) and will rev out to 3000 revs in reverse before black smoke. Engine starts first go, runs smoothly and normally up to the problem revs. Everything else appears normal (i.e temp, oil level and colour etc, air filter is completely clean)

I have discounted over-propping issue as I have a three blade fixed prop that has been on the boat for over a year before I experience the smoke issue and has always ran normally. Engine/shaft Alignment is perfect, Filters have been checked/replaced, tank appears clean and has always been treated when filled.

Could this be a clogged exaust elbow issue, or more likely injector, injector pump or lift pump problem?

any thoughts would be appreciated

[centaursailor]

Hi, Could be a lot of things, probably not the injection pump or fuel system as this general produces gray exhaust when faulty.
Soot is unburnt fuel Tappet settings should be checked as this can contribute to poor valve operation and inspection of the valves and seats often shows the problem. . Check cylinder pressures for signs of head gasket failure, pressures should be fairly even.A good mechanic would be worth consulting as the engine is relatively new and should not be giving problems unless its been used under small load for long periods as this leads to bore glazing and can produce similar symptoms.Always work within your skill set as the engine is a complex and expensive piece of kit and basic knowledge is needed for any of these suggestions.
Hope this helps.
Brian

[Lathe]

Thanks for that. Have just removed the exhaust mixer elbow and it is clogged with carbon, leaving only 40-50% of the normal diameter for the exhaust gas to escape through, so could explain the lack of power when under load due to back pressure. Going to replace it as most Yanmar forums say 3 years is about the service time for the elbow, so hopefully this is the problem.

[Minnewaska]

I would want to know why the elbow had build up that severe in such a short period of time. Replacing the elbow may only temporarily fix the symptom, not the disease.

[boatpoker]

The 3YM30 has had issues with overheating due to a poor heat exchanger design. This issue affected all engine numbers below 05566
Link to Service Advisory .... http://www.pcmarinesurveys.com/Yanma...20advisory.pdf

[Faster]

Originally Posted by Lathe

Could this be a clogged exaust elbow issue, or more likely injector, injector pump or lift pump problem?

any thoughts would be appreciated

Lathe

Well presented original post, and it looks like you may have answered your own question.

btw as to a faulty injector, unless it's completely clogged, a bad injector usually produces an loud ticking sound (as you try to compress unatomized fuel), a slight rpm increase, and dirty BROWN smoke. It's disconcerting because it actually sounds like internal metal-on-metal contact.

[Lathe]

Originally Posted by Minnewaska

I would want to know why the elbow had build up that severe in such a short period of time. Replacing the elbow may only temporarily fix the symptom, not the disease.

I have only owned the boat a little over 12 months and although I use the engine a lot and run it at 3000rpm for cruising speed, the previous owner only used the boat for racing and told me that he only ran the engine around 2200 revs. This could explain the carbon, as engine was not being run under enough load with the old owner. I am probably also partly to blame, as I have been unable to take the boat out over the past couple of months due to other committments and have used the engine to charge the batteries several times due to lack of shore power. Although I put it into gear in the marina, I only run it up to 2000rpm. Probably not the best thing now in hindsight to be doing!

new elbow going on today, will let everyone know the outcome. The Yanmar forums I have been on as well as other owners with Yanmars I have spoken to reckon the elbows do not last long, only a few years and will also easily carbonize if not run under load.

[rk6johnson]

I have a previous post with a similar problem. Engine would only rev to 1500. After removing and reworking Injectors and pump, checking compression, etc, we also discovered the soot filled elbow and exhaust outlet. This cost me $1500 in service with 20 hours or so! Wish I had seen this thread a month ago. At that time, best advice was to check filter in tank! Seems this is a common problem in this engine. We have only 360 hours on 2008 Catalina 309.

[Lathe]

Thanks to all for the thoughts/comments

Engine is fully cured. It was the clogged exhaust elbow that caused the problem. Can now get full RPM with no smoke and engine is much quicker to respond to throttle movements. I would say that is was a problem that started before I bought the boat that has progressed with time.

Luckilly for me, problem was a cheap one to fix ($20 for the engineering shop to put the hydraulic wrench on to get elbow apart). To anyone experiencing similar symptoms with lack of RPM and Black Smoke, check the exhaust elbow before you pull injectors and get serious with the engine etc It may save you a lot of money!!

[CapitainMike]

Originally Posted by Lathe

Thanks to all for the thoughts/comments

Engine is fully cured. It was the clogged exhaust elbow that caused the problem. Can now get full RPM with no smoke and engine is much quicker to respond to throttle movements. I would say that is was a problem that started before I bought the boat that has progressed with time.

Luckilly for me, problem was a cheap one to fix ($20 for the engineering shop to put the hydraulic wrench on to get elbow apart). To anyone experiencing similar symptoms with lack of RPM and Black Smoke, check the exhaust elbow before you pull injectors and get serious with the engine etc It may save you a high rise elbow.

Also worth checking is the prop going clockwise when looked at from the stern. Why you say? I have known a case where a previous owner had clobbered his prop and to save money prior to the sale the controls were altered so that ran in reverse and an old left hand prop was installed. you can imagine the consequences.