Yanmar 3GM30 Ehaust-manifold/mixing ellbow and anti-siphon

[Tranona]

Re: Yanmar 3GM30 Ehaust-manifold/mixing elbow clogged

That is not uncommon and probably results from running the engine on too light load for too long. These engines need to get hot and run hard otherwise deposits build up in the exhaust outlet where the salt water is injected into the exhaust gas.

So have it cleaned out and then always make sure that you run the engine at 60-70% maximum revs, so for your engine around 2200-2400 rpm and as recommended in the hand book run for short periods regularly at full rpm

 

[VicS]

Re: Yanmar 3GM30 Ehaust-manifold/mixing elbow clogged

Hello,
This thread seems as close to what my issue is as anything, without starting a new one (how does one do that anyway?)
Has anyone seen this happen to your yanmar 3ym30 exhaust manifold/elbow (inverted U shaped)? My engine is 3 years old(Feb 2014 install) has only 200 hrs on it. The boat has been hauled out every year by the beginning of a hurricane season and saltwater cooling flushed out with fresh water religiously, every time, once on the hard. Then I would disconnect the exhaust hose and stuff a rug into the elbow exit and cover with plastic and secure it with a rubber band so no water or salty air gets blown into the manifold.
What you see in the pictures is salt crystals mixed with something resembling a very fine white powder (aluminum oxidation?). Mechanic that did the installation is as befuddled as I am. Does that section need a yearly maintenance? Have not seen that being mentioned in the service/user manual.
Any ideas and help greatly appreciated

It would have been preferable to have started a new thread of your own rather than resurrecting an 8 year old one and adding you post to it.

You start a new thread by clicking on the "Post New Thread" button at the top of the index page see here http://www.ybw.com/forums/forumdisplay.php?13-Practical-Boat-Owner-s-Reader-to-Reader


As for your exhaust system problem.

The white powder is aluminium oxide with little doubt

You do not say how you are flushing the seawater system. It would best if the engine drew the water up from a bucket so that as soon as you stop the engine the water flow stops. Are you force feeding it from a hose and allowing the water flow to continue for a short time after stopping the engine? If you are doing this you may be getting water into the manifold and then sealing it in with your rag and plastic bag !

Also wondering if your engine is fitted with a vented antisyphon loop in the seawater system? Ok not necessary if the injection point into the elbow is well above water level but if not you could be getting water siphoning in on regular basis.

 

[vyv_cox]

Re: Yanmar 3GM30 Ehaust-manifold/mixing elbow clogged

Unless the 3YM is made very differently from the 3GM it is difficult to understand where aluminium oxide is coming from. There is no aluminium on the seawater side of my 3GM and only a couple of nozzles on the coolant side. I would be tempted to say that what you have is a mixture of carbon and salt, quite possibly resulting from light use as Tranona suggests. I have seen such mixtures in other engines, also aluminium-free.

 

[VicS]

Re: Yanmar 3GM30 Ehaust-manifold/mixing elbow clogged

Unless the 3YM is made very differently from the 3GM it is difficult to understand where aluminium oxide is coming from. There is no aluminium on the seawater side of my 3GM and only a couple of nozzles on the coolant side. I would be tempted to say that what you have is a mixture of carbon and salt, quite possibly resulting from light use as Tranona suggests. I have seen such mixtures in other engines, also aluminium-free.

I was assuming that the HE/ exhaust manifold was aluminium

 

[vyv_cox]

Re: Yanmar 3GM30 Ehaust-manifold/mixing elbow clogged

I was assuming that the HE/ exhaust manifold was aluminium

Hence my first line on the differences between the two engines. On the 3GM everything is stainless steel, but I know that aluminium manifolds are increasingly being used, so I don't know.

Have to agree, in the OP's photos the manifold looks like a casting that could be aluminium.

 

[RichardS]

Re: Yanmar 3GM30 Ehaust-manifold/mixing elbow clogged

That is not uncommon and probably results from running the engine on too light load for too long. These engines need to get hot and run hard otherwise deposits build up in the exhaust outlet where the salt water is injected into the exhaust gas.

So have it cleaned out and then always make sure that you run the engine at 60-70% maximum revs, so for your engine around 2200-2400 rpm and as recommended in the hand book run for short periods regularly at full rpm

I can't really add to the thoughts already posted, other than say that my 3YM30s are clean as a whistle at that point so it's definitely not "normal" behaviour.

However, on my engines the elbow curves downwards after the flange and the cooling water is then injected into a double skinned section so the actual point where the water meets the exhaust gas which is where the double-skin ends is 4 inches after the flange and a couple of inches below it. I therefore cannot see that there is any way that water is getting anywhere near the manifold flange so whether the water runs through aluminium or not does not seem relevant.

It should be just hot exhaust gas passing that flange so if there is water there, and it does look like there is, then it is either coming through the combustion chambers through a leaking head gasket or similar, which seems very unlikely and the OP would notice the coolant level going down, or all the blocking of the exhaust system is being done whilst the system is still being flushed and the water trap is filling with water which is finding its way back up through the elbow and into the manifold. However, in that event, I would expect some of it to have potentially found its way past an exhaust valve and wrecked the engine.

If the water level was just enough to reach the manifold but not enough to enter the cylinders, the OP has been extremely fortunate.

Richard

 

[VicS]

Re: Yanmar 3GM30 Ehaust-manifold/mixing elbow clogged

I can't really add to the thoughts already posted, other than say that my 3YM30s are clean as a whistle at that point so it's definitely not "normal" behaviour.

However, on my engines the elbow curves downwards after the flange and the cooling water is then injected into a double skinned section so the actual point where the water meets the exhaust gas which is where the double-skin ends is 4 inches after the flange and a couple of inches below it. I therefore cannot see that there is any way that water is getting anywhere near the manifold flange so whether the water runs through aluminium or not does not seem relevant.

It should be just hot exhaust gas passing that flange so if there is water there, and it does look like there is, then it is either coming through the combustion chambers through a leaking head gasket or similar, which seems very unlikely and the OP would notice the coolant level going down, or all the blocking of the exhaust system is being done whilst the system is still being flushed and the water trap is filling with water which is finding its way back up through the elbow and into the manifold. However, in that event, I would expect some of it to have potentially found its way past an exhaust valve and wrecked the engine.

If the water level was just enough to reach the manifold but not enough to enter the cylinders, the OP has been extremely fortunate.

Richard

The OP has the inverted U shaped exhaust bend though.... what others might call a "riser" ? I dont know its construction but I assume the water finally enters the gas stream on the" down hill" side, in a similar way to yours, otherwise it would tend to fill the manifold.
https://www.manualslib.com/manual/825607/Yanmar-3ym30.html?page=166#manual

As you say there should only be exhaust gas passing that flange. There should not be any water at that point. If the deposit is a mix of salt and carbon then one has to wonder where the salt is coming from.

 

[RichardS]

Re: Yanmar 3GM30 Ehaust-manifold/mixing elbow clogged

The OP has the inverted U shaped exhaust bend though.... what others might call a "riser" ? I dont know its construction but I assume the water finally enters the gas stream on the" down hill" side, in a similar way to yours, otherwise it would tend to fill the manifold.
https://www.manualslib.com/manual/825607/Yanmar-3ym30.html?page=166#manual

As you say there should only be exhaust gas passing that flange. There should not be any water at that point. If the deposit is a mix of salt and carbon then one has to wonder where the salt is coming from.

Ah yes. I see it's a proper inverted U rather than my opened-out inverted U. I see mine is called and L-type rather than a U-type, although even Yanmar seem to have got themselves confused on their own diagram.

As you say, it must be a double skin and the double skinning must surely end close to the downstream end of the U. If it isn't double-skinned and the water injection is at the point shown in the diagram then I would expect some water to always drop back into the flange which might explain the problem. However, surely Yanmar would not have designed it like that?

However, whereas the L-type is "failsafe" so that even if the double-skinning develops an internal leak, the water injection point is always downhill from the manifold, the U-type appears to be non-failsafe and a corroded elbow would allow water to drain back to the manifold flange.

Is an internally corroded inner-skin the source of the problem?

Richard

 

[janabr]

Re: Yanmar 3GM30 Ehaust-manifold/mixing elbow clogged

Thank you VicS for the tip on starting new thread and on the vented anti-syphon.
Yes, flushing is done with the intake hose removed from the drive for that purpose and extended to reach the bucket of fresh water with water added continuously to allow several bucketfuls of fresh water per flush. Engine is then stopped. Rag and plastic barrier is put on after flushing is completed. One would hope not much salt water should be left in the system after the flush.
The elbow is definitely above water level but maybe not that much. In rough conditions it may occasionally dip below. Must look into this. The seawater tubing goes from the heat exchanger up to a vented antisyphon U (some two feet or so above hexch) and comes down to the elbow injection point. I am even eyeing my water muffler now thinking maybe it is not big enough. Installation mechanic seems to have done all by the book, or did he?

 

[knuterikt]

Re: Yanmar 3GM30 Ehaust-manifold/mixing elbow clogged

Don’t know the make of your waterlock but Vetus have a sizing based on length and diameter of exhaust hose.
If anti siphon is fitted check that it’s working.

 

[janabr]

Re: Yanmar 3GM30 Ehaust-manifold/mixing elbow clogged

Thank you Tranona for your suggestions. Greatly appreciated.

 

[VicS]

Re: Yanmar 3GM30 Ehaust-manifold/mixing elbow clogged

Don’t know the make of your waterlock but Vetus have a sizing based on length and diameter of exhaust hose.
If anti siphon is fitted check that it’s working.

+ 1 on both of those points

The formula for calculating the size of the water trap can be found on page 83 of the on line Vetus catalogue http://viewer.zmags.com/publication/d5cab42f#/d5cab42f/82

 

[janabr]

Re: Yanmar 3GM30 Ehaust-manifold/mixing elbow clogged

Than you all for the suggestions.