Yanmar Exhaust Elbow - Source of leak?

[bostonbubba]

Hello,


Long time lurker, finally posting. Running into an issue with an exhaust elbow for a Yanmar 2GM20F that I could use some input on.



I replaced the exhaust riser, coupling, and exhaust elbow at the beginning of last season as the old one had reached the end of its lifespan. Everything ran great last summer through winterization. Fast forward to this season, replaced the impeller, recommissioned the engine, and everything looked fine again. However, now I am getting a small leak at the coupler junction (the double threaded piece that connects the riser to the elbow).



Thoughts on where is the water coming from?



In theory, there shouldn't be any water at that junction, just exhaust. Water is coming out the exhaust at the transom as expected. I pulled everything off to have a look and the elbow looks fine, no cracks/holes. I put it back together with Hercules Real-Tuff teflon thread sealant (hand tightened with a 90 degree bend), put it back on and still same issue. The engine appears to be running fineI am wondering if there might be some sort of blockage in the wet exhaust hose further down stream but then why would water still be coming out? I could run a snake from the muffler back to see if there is any thing in there.


Any thoughts would be greatly appreciated. Thanks in advance.

[GordMay]

Greetings and welcome aboard the CF, Bubba.

[gonesail]

not an expert but I would assume the joint is not tightened enough. also Yanmar warns against wrenching this joint while it is still connected to the manifold.

[bostonbubba]

gonesail - thanks for the reply and input. I had hand tightened it with the whole thing pulled off the engine. I will give it another try and see if I can tighten the top portion of the coupler/elbow a bit more.

[bratzcpa]

i replaced my exhaust elbow a few years ago (3gm30). If I remember correctly, that nipple has reverse threads on one end. This allows you to simply tighten it up a bit will everything is still hooked up.

In other words, you don't have to take off the exhaust hose and work backwards.

I would, however, be careful not to apply too much force when tightening. Use a pipe wrench and go easy. You surely don't want to damage the exhaust manifold.

[a64pilot]

I think I would call Mack Boring or another good, reputable Yanmar dealer and ask a mechanic, cause if I understand, the issue isn't why is it leaking so much, as why is there water, where there shouldn't be?

I'd want an answer to that before I ended up with a hydrolocked motor

[bostonbubba]

a64pilot - I am thinking along the same lines. If I am understanding the internals of the elbow correctly, not sure how water would get from the sea water inlet down into the hot exhaust inlet (exhaust and water inlet are two separate chambers that meet at the cooled exhaust outlet). Maybe there is a hairline crack in the elbow somewhere. More investigation is warranted.



Thanks for the info.

[Tusitala]

It's a wet exhaust, water flows through the manifold and that is the mixing elbow elbow. the Yanmar shop I use gets a kit that includes the entire assy, the manifold and elbow, preassembled. they told me that connection can be a bit problematic to seal so they just replace the entire setup. you may have to take it apart and use sealant on thethreads.

[roverhi]

Originally Posted by bostonbubba

gonesail - thanks for the reply and input. I had hand tightened it with the whole thing pulled off the engine. I will give it another try and see if I can tighten the top portion of the coupler/elbow a bit more.

What is HAND tightened?? Should have used a pipe wrench with the assembly held in a good vice. Pipe threads require a goodly amount of torque to be sure that you get a seal. Think the reason than Yanmar says not to assemble disassemble in place because of the torque on the exhaust riser needed to ensure a seal. Getting it apart is another story. Tried changing mine with two large pipe wrenches, cheater bar, and a friend helping without success. Had to call in the Calvary that game with a humongous vice, torch, even bigger pipe wrench with cheater bar and it was still a bitch to get apart.

[bostonbubba]

roverhi - thanks for the input. When fully tightened, the exhaust riser and elbow are at 180 degrees (straight line). I need a 90 degree bend so either side of the coupling won't be fully tight when at 90 degrees. My guess is that I haven't used enough "goop" on the threads and I haven't tightened it enough. Will try both.

[AA3JY]

We replaced our Yanmar exhaust elbow with one of these..

https://hdimarine.net/product/gm-sta...-mixing-elbow/

[JimsCAL]

Originally Posted by bratzcpa

i replaced my exhaust elbow a few years ago (3gm30). If I remember correctly, that nipple has reverse threads on one end. This allows you to simply tighten it up a bit will everything is still hooked up.

In other words, you don't have to take off the exhaust hose and work backwards.

I would, however, be careful not to apply too much force when tightening. Use a pipe wrench and go easy. You surely don't want to damage the exhaust manifold.

On my 3GM30F there is a coupling that has right hand threads on one end and left hand threads on the other. This allows tightening with the elbow at any angle and without need to rotate the elbow. Just turn the hex on the coupling.

[wsmurdoch]

But, I still don't understand why the OP has water on the inlet side of the Yanmar exhaust elbow. The elbow is designed so that the water injected into the elbow goes out the outlet of the elbow.

Other than the initial condensation of water vapor in the exhaust on cold metal before everything heats up, why is liquid water in the left-hand/right-hand threaded nipple that is on the inlet side?

[bostonbubba]

AA3JY - I have the exact same one except I got the riser as well (HDI sells a kit)


JimsCAL - I tried that but one half is always not at full tightness. When I asked HDI if the could tighten prior to shipping, they said they could only tighten it straight.


In poking around the interwebs, I found this article that seems to suggest the same thing:


The opposing threads on the connector are supposed to draw the two elbows together as it’s tightened, but I found that the mixing elbow was about a quarter-turn adrift of its optimum position after the riser was snugged tight. A healthy glob of high-temperature exhaust sealant was applied to the threads, and the assembly was left overnight to dry. It had set rock hard by the morning.


https://www.sailmagazine.com/diy/mai...diesel-exhaust

[bostonbubba]

wsmurdoch - when I noticed the leak, the engine maybe had only been running for a couple of minutes. The elbow was warm but not hot. Not sure how long it would need to run to burn off the initial condensation.