black water from exhaust

[boo1966]

Just noticed that there is something turning the water from my exhaust black.Engine seems to be running fine starts and goes but there is a lot of what seems like carbon soot (not oily)mixed with the water also there seems to be white smoke coming from the exhaust also.(head gasket ?)
Any ideas?
Cheers

 

[alan17]

It may just be soot from the inside of the exhaust.
Does the white smoke hang around or disipate very quickly. If it hangs around it could well be a head gasket problem or an injection problem. (Unburnt diesel but this would usually leave a film on the water surface)
If it disipates very quickly it may simply be steam created by the water cooling the exhaust gases.

 

[oilyrag]

Not a Yanmar 1GM10 perchance?

 

[boo1966]

Good guess Oilyrag Yanmar 1gm 10.I pulled the complete exhaust system out over the winter quite alot of black grit in the boxes.The white smoke/steam vanishes immediately but the black soot keeps coming .Im thinking bad combustion unburnt fuel or oil getting into the cylinder burning then getting spat out the back but there is no oilslick behind the boat.

 

[Moonshiners]

it's not "cleaning crap" burning off that you used when you had it apart over winter is it? id you change any part of the exhaust, that would make a part of it hotter/cooler than it was before?

 

[oilyrag]

Not much of a guess I'm afraid Boo - what you describe are classic symptoms of the 1GM10 disease that has been done to death every season on this forum for god knows how long. But as a relative newbie, and as no one else has picked up on it yet, I will run it by you:
The Achilles Heel of the 1GM, amongst several other more minor ideosynchracies, is the exhaust elbow. It is a pipe within a pipe affair with the outer pipe carrying the cooling water via the water injection point on top of the elbow and the inner pipe which is the actual exhaust pipe. The inner pipe corrodes, unseen and unknown to the owner, who sees a lovely shiny outer pipe and guffaws loudly at any suggestion that the elbow is rotten. Once the inner pipe is perforated, the cooling water gets sucked back into the engine via the exhaust port causing accelerated corrosion to the port, which in a worse case ultimately corrodes through into the pushrod channels. In the meantime, before this final stage is reached, the water being drawn back into the cylinder will be emitted from the exhaust as steam. This steam scours the inside of the exhaust carrying away with it the carbon deposits from the exhaust port and pipe - and hence the symptoms you describe. The only other clue to this is the likelyhood of hydraulic lock when starting due to the coolant condensing in the cylinder after stopping the engine. On attempting to restart it won't initially turn over until the water is cleared. This can cause a bent con rod (or as someone pointed out recently a squashed con rod but who cares, it's fecked either way) and/or a blown head gasket (which will add to the steam content emitted from the exhaust).

To verify this, take the exhaust elbow off the engine, and turn it so that you are looking down the end where you can see the inner pipe (i.e. the opposite end from the flange). Put your finger over the injection pipe, and carefully fill the inner pipe with water. If the elbow is OK, nothing will happen - i.e. you will be standing holding a pipe with an inner pipe full of water. What I will expect you will find is that the water will trickle through and out of the inlet (flange/engine) end of the elbow. This demonstartes that the inner pipe is perforated and fecked. If so, look at the exhast port in the cylinder head - instead of a nice regular shaped port around 5/8" diameter, you will see a bigger horrible rusty irregular shaped hole. If so, take the head off - a straightforward 30 minute job - and check it over. You may find corroded exhaust valve, blown head gasket (look for tracking between the cylinder hole and coolant channel passage). If you are lucky, you may get away with a new elbow and head gasket. Otherwise you are looking at a new cylinder head as well - around 400 notes. There is also a chance as mentioned of a damaged conrod although if it is currently still starting this may not be the case. The symptom is poor starting due to lack of compression.
Take a look at it sooner rather than later and let us know how you get on.

 

[boo1966]

Nothing changed just hosed it out and back in again

 

[mikehibb]

What revs does this happen at?

I had a similar looking pool of black sooty water emit from my yanmar (3GM27F) last week a couple of times. It only occured when giving some serious revs. I assumed that It was just clearing out some soot and needed a good clear out.

The engine has not had any hard work for a while, last big run was a 12 hour delivery motorsailing at 2400 rpm.
Many people say that the yanmars need a good hard drive regularly.

I had been pootling around at similar revs, slowly inceasing to 3000 revs no probs, but give it a bit of max throttle and it puffs out the soot.

As I found out when full astern after the wind caught me whilst trying to berth. Just missed clipping the end of the pontoon.
But a miss is as good as a mile.

First time the engine had been run at full revs under load for a while I guess (new to me boat) Next trip I will give it a good hard run.

 

[oilyrag]

Sounds like your boat is over-propped - it should rev up to 3400-3600 at full throttle.

 

[boo1966]

Thanks very much everyone will have a look at the exhaust elbow and cylinder head and report back Cheers