the last time my yanmar 2gm20 mixing elbow clogged, i had the yanmar guy change it. this time, i want to do it myself. if i remember correctly, the union between the elbow and the exhaust manifold is the kind of two-directional screw that pushes the parts apart or pulls them together as you turn it with a wrench. when installing a new mixing elbow, do the threads need to be coated with pipe dope or tape? if so, what kind? also, what about the little elbow fitting that connects the raw water hose to the elbow? does it need to be pipe doped, and with what kind. lastly, can these things be cleaned out? if so, what's the best way? thanks!
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Mixing elbow
Don, I just did mine. You are correct about the union. One side is right hand thread, the one that goes to the exhaust maniford, and the other, which screws to the elbow itself, is left hand thread. I threaded on the side that goes on to the manifold until it was tight. Then I threaded on the elbow until it too was tight then backed the elbow off to align it correctly to fit on the exhause hose. I used high temp RTV as a thread sealant but I guess you can use regular pipe thread sealant. The new elbow already had the cooling water connection installed - I believe that is how its shipped from Yanmar. With respect to cleaning, the elbow can be cleaned using a small chisel and some elbow grease. I opted to get a new elbow because I was concerned that chiseling may have ruptured the wall that separates the gases and water prior to the point where they mix on the down hill side of the elbow. If the wall is ruptured, cooling water could end up in the cylinders when the engine is stopped instead of flowing down the exhaust hose and into the silencer.
Don, I just did mine. You are correct about the union. One side is right hand thread, the one that goes to the exhaust maniford, and the other, which screws to the elbow itself, is left hand thread. I threaded on the side that goes on to the manifold until it was tight. Then I threaded on the elbow until it too was tight then backed the elbow off to align it correctly to fit on the exhause hose. I used high temp RTV as a thread sealant but I guess you can use regular pipe thread sealant. The new elbow already had the cooling water connection installed - I believe that is how its shipped from Yanmar. With respect to cleaning, the elbow can be cleaned using a small chisel and some elbow grease. I opted to get a new elbow because I was concerned that chiseling may have ruptured the wall that separates the gases and water prior to the point where they mix on the down hill side of the elbow. If the wall is ruptured, cooling water could end up in the cylinders when the engine is stopped instead of flowing down the exhaust hose and into the silencer.
Use never sieze.
Don: If you look in the photo forum you may be albe to find my photo forum article on the subject. You need to use never sieze compound on the threads for the manifold & the union. I never took mine apart again so I do not know how well this stuff works, but it is a common item for mechanics to use on part like the exhaust manifold or anything that gets super heated on an engine.
Don: If you look in the photo forum you may be albe to find my photo forum article on the subject. You need to use never sieze compound on the threads for the manifold & the union. I never took mine apart again so I do not know how well this stuff works, but it is a common item for mechanics to use on part like the exhaust manifold or anything that gets super heated on an engine.
Thread Lubricant
Steve - My experience with Never-Seze in the mixing elbow threads was that it MAY have caused them to sieze even worse. This is hard to tell because the amount of torque in tightening the coupling has a lot to do with it too and I admit it may have been tightened more than it should have. My guess is the metalic stuff in the Never-Seze may not be good for high temperature. This time I used Champion (the spark plug company) aircraft "No. 2612 Spark Plug Thread Lubricant" and is designed for high temperature threaded connections. See link: http://www.championaerospace.com/tool16.htm. I used this on my plane which had an air-cooled engine and consequently the cylinder heads could get quite hot. My reasoning is, since the mixing elbow threads are in a similar environment it should work like it does on spark plugs. Also, this time I tightened the coupling the minimum necessary to keep it together without coming apart. Hopefully this will make it easier to take apart next time. The possible downside to this idea may be that carbon, say, could find its way up the threads a tad and consiveably actually make matters worse. We'll see. I also have Never-Seze but use it on room-temperature things like screws in the mast, and the like. Steve - I'd be interested how your coupling comes apart next time as compared to previous times.
Steve - My experience with Never-Seze in the mixing elbow threads was that it MAY have caused them to sieze even worse. This is hard to tell because the amount of torque in tightening the coupling has a lot to do with it too and I admit it may have been tightened more than it should have. My guess is the metalic stuff in the Never-Seze may not be good for high temperature. This time I used Champion (the spark plug company) aircraft "No. 2612 Spark Plug Thread Lubricant" and is designed for high temperature threaded connections. See link: http://www.championaerospace.com/tool16.htm. I used this on my plane which had an air-cooled engine and consequently the cylinder heads could get quite hot. My reasoning is, since the mixing elbow threads are in a similar environment it should work like it does on spark plugs. Also, this time I tightened the coupling the minimum necessary to keep it together without coming apart. Hopefully this will make it easier to take apart next time. The possible downside to this idea may be that carbon, say, could find its way up the threads a tad and consiveably actually make matters worse. We'll see. I also have Never-Seze but use it on room-temperature things like screws in the mast, and the like. Steve - I'd be interested how your coupling comes apart next time as compared to previous times.
I cleaned mine yesterday
I was moving my boat Saturday, but almost out to the channel, my Yanmar overheated. So I had my boat towed back into the marina. To make the story short, no mechanic was available Saturday, and after I verified that everything was OK upto the mixing elbow, I went home to research the problem. Thanks to this forum, I concluded that the problem is in the mixing elbow. Sunday moring, I tried to separate the elbow & the exhaust pipe. Not easy. So I removed the whole thing from the exhaust manifold. Remove the hose connector, then use long, thin screwdriver to scrape both from the elbow opening and the opening where the hose connector screws in as far as I could. Then I run water into each of the openings. I can't tell, but it seems the exhaust airway was not a problem. It was just the water path was blocked. But I can't imagine that by just scrapping the openings with a screwdriver and running water through them un-blocked it. There must be not that much of water pressure after going through the heat exchanger? Anyway after observing that there was plenty of water going through the hose connector opening, I attached everything back together, run the engine and found that tons of water was pushed out of the exhaust port, but more importantly, the sea water hoses stayed cool, the heat exchanger stayed warm (not hot). I was like in heaven, got going right away, and was able to move my boat 40 miles from the Everett back into lake Washington. Like I said, my mixing elbow did not seem to be that plugged up. So I am not sure if it's easy enough to just do some scraping and run water through it to clear it, or I was just lucky. Anyone know if anyone sells flexible brushes that can be used in this case? I certainly will keep an eye on this mixing elbow, run the engine hard like many advised, and remove the whole thing at least once a year just to make sure the air/water paths are clear.
I was moving my boat Saturday, but almost out to the channel, my Yanmar overheated. So I had my boat towed back into the marina. To make the story short, no mechanic was available Saturday, and after I verified that everything was OK upto the mixing elbow, I went home to research the problem. Thanks to this forum, I concluded that the problem is in the mixing elbow. Sunday moring, I tried to separate the elbow & the exhaust pipe. Not easy. So I removed the whole thing from the exhaust manifold. Remove the hose connector, then use long, thin screwdriver to scrape both from the elbow opening and the opening where the hose connector screws in as far as I could. Then I run water into each of the openings. I can't tell, but it seems the exhaust airway was not a problem. It was just the water path was blocked. But I can't imagine that by just scrapping the openings with a screwdriver and running water through them un-blocked it. There must be not that much of water pressure after going through the heat exchanger? Anyway after observing that there was plenty of water going through the hose connector opening, I attached everything back together, run the engine and found that tons of water was pushed out of the exhaust port, but more importantly, the sea water hoses stayed cool, the heat exchanger stayed warm (not hot). I was like in heaven, got going right away, and was able to move my boat 40 miles from the Everett back into lake Washington. Like I said, my mixing elbow did not seem to be that plugged up. So I am not sure if it's easy enough to just do some scraping and run water through it to clear it, or I was just lucky. Anyone know if anyone sells flexible brushes that can be used in this case? I certainly will keep an eye on this mixing elbow, run the engine hard like many advised, and remove the whole thing at least once a year just to make sure the air/water paths are clear.
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