Yanmar Black Smoke

[Astrid]

I would see about taking the intake manifold off and make sure nothing was still in there to restrict air flow. I had something similar happen on an old Jeep engine that had an oil bath air filter. It never seemed to develop as much power as I thought it should (for its age anyways) and when I took the air filter off, I found that it had a piece of oil soaked rag that had gotten caught up in the intake pipe below the oil filter. Once that was removed and the oil filter thoroughly cleaned there was a marked improvement.

[rgleason]

Last fall our engine began blowing black smoke at 2100 rpm, and the engine acted like it was under load. New injectors were the solution for us. The old injectors were rebuilt about 1998. But the foam might be the problem. Rick

[Scallywag627]

I've had the boat for several years. Use it a couple of time a month. Foam disintegration around the yanmar filter/ silencers is nothing new. Happens to diesels all the time. No smoke in neutral only in drive at high Rpms. I'm thinking crud on the bottom, but I will be checking the filters, although if it were the filters it seems like it would also smoke in neutral .

[Sailmonkey]

Usually, clogged filters will cause a loss of power, but not smoke. Black smoke is a condition caused by unburnt fuel or an overloaded engine.
If the injectors are not atomizing correctly then as the throttle increases you may actually get a fuel stream instead of a fuel mist. Streams don't burn.

[Ex-Calif]

Originally Posted by Scallywag627

I've had the boat for several years. Use it a couple of time a month. Foam disintegration around the yanmar filter/ silencers is nothing new. Happens to diesels all the time. No smoke in neutral only in drive at high Rpms. I'm thinking crud on the bottom, but I will be checking the filters, although if it were the filters it seems like it would also smoke in neutral .

- Dirty fuel
- Defective injectors
- injection timing off
- too much fuel scheduled
- blocked intake/filter
- blocked exhaust
- overloaded engine - hull/prop dirty or rope wrap

I think you are now hinting that the bottom is dirty. It is surprising how little fouling is needed to load the engine depending on the engine hp vs. boat weight vs. prop pitch.

Many boats with a little spare hp and a lower pitched prop are very tolerant of fouling.

[Snkr]

Originally Posted by Sailmonkey

Usually, clogged filters will cause a loss of power, but not smoke. Black smoke is a condition caused by unburnt fuel or an overloaded engine.
If the injectors are not atomizing correctly then as the throttle increases you may actually get a fuel stream instead of a fuel mist. Streams don't burn.

Actually white smoke is evidence of unburnt fuel! Just saying.

[Ex-Calif]

Originally Posted by Snkr

Actually white smoke is evidence of unburnt fuel! Just saying.

It can be but other (bad things) are more likely - I would agree white smoke is "unburned" (raw fuel) and black smoke is "poorly burned" fuel i.e. the combustion takes place but the combustion is not "complete" due to some other reason.

White Smoke -
Lack of compression
Water in fuel
Air in fuel
Defective injector
Water in cylinder - cracked head or leaking head gasket.

[Sailmonkey]

Originally Posted by Snkr

Actually white smoke is evidence of unburnt fuel! Just saying.

You're right, I was wrapping my skull around other things at the moment and went to typing without proofreading with my brain.......

[chef2sail]

In addition to the other suggestions this one caused our 3GM30 to have the exact same problem. The oil was overfilled. Check on the oil level. Have you changed it recently.

Dave

[Albro359]

Smoke
Black : Obstruction in airflow - air filter issue, High exhaust backpressure
Excessivel;y high ambient temperature
Overload - rope around the prop. oversized prop, heavily fouled bottom
Defective infection system

from Nigel Calder.....

[Capt.Fred]

Originally Posted by Albro359

Smoke
Black : Obstruction in airflow - air filter issue, High exhaust backpressure
Excessivel;y high ambient temperature
Overload - rope around the prop. oversized prop, heavily fouled bottom
Defective injection system

from Nigel Calder.....

Albro, you are right on. Black is as described above. Also,
White is usually timing and/or cold engine.

[dougwm10]

I have a Yanmar diesel which has recently had new piston rings fitted and the injectors cleaned. It now emits pale wisps of bluish smoke when idling which get progressively denser when the revs are increased.

Any ideas or thoughts on the reasons why

[Albro359]

Blue smoke = oil burning
Given that you have new piston rings...were the bores checked for scoring before fitting ?..they really should have been honed before fitting the new rings
Other possibility is worn valve guides in the head

Or more simply too much oil in the crankcase or exccesively high oil pressure?

[rgleason]

Black smoke - 3GM30... The oil was overfilled. Check on the oil level. Have you changed it recently.

Good point.

[Ex-Calif]

Originally Posted by dougwm10

I have a Yanmar diesel which has recently had new piston rings fitted and the injectors cleaned. It now emits pale wisps of bluish smoke when idling which get progressively denser when the revs are increased.

Any ideas or thoughts on the reasons why

How long ago in engine operating hours?

I am old school and feel the engine should be run hard (>3/4 throttle) for at least 10 hours after a ring change. But depends...

Chrome rings and steel cylinders. If the bore was honed properly there is a "matrix" of scratches on the walls that helps retain a film of oil. If you run easy the oil can glaze and you get too smooth a bore and the rings never seal properly.

Also while running in I like to vary the throttle from 3/4 to almost full throttle every 15 minutes. Short runs (5 minutes in and out of a marina) are a no go during break in.

If new rings were fitted and the cylinders not honed all bets might be off.

YMMV...