Exhaust Elbow R&R

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    David C Morris

    Found a minor drip under the bottom of the exhaust elbow and so it was time to remove, inspect and possibly replace the elbow and the section of exhaust hose between the elbow and muffler.  It took me a number of days to “persuade” the (4)  8mm-1.25mm, 10.9 bolts to release their grip.  Kroil helped and using a 6 point 10mm wrench was essential.  The elbow seemed to be in pretty OK condition and no real damage was noted inside the 6 inch exhaust hose.  The turbo spun freely and so I cleaned up the turbo mounting surface, chased the threads and mounted the new elbow I had purchased from S&B Marine.  We decided to use the higher temperature exhaust hose (Blue) which resulted in needing (4) new (slightly shorter) t- bolt clamps.  Red Hi Temp RTV and some anti- seize compound rounded out the supply list.  It went back together easier than it came apart and we tested it for leaks today.  All OK!  Glad to have that little chore over and done.

    Tom Easterbrook


    I am very happy that your “project” worked out OK and that it appears you have SO FAR avoided any saltwater damage to your turbo or worse yet your engine. Good choice going with the “blue hose”. You and anyone else who has this type of exhaust elbow (and similar setup), should read my post titled “Important Maintenance for Cummins 6BTA” on this site (the info could apply to other engines as well).

    The exhaust system as shown in the photo is not well designed, and could lead to big problems for some unlucky owners. Big problems caused by saltwater (or fresh, but not as bad) being able to migrate into the turbo and sometimes even into the exhaust side of the engine itself (in the worse case needing a new engine or a complete rebuild). Tony Athens (owner of Seaboard Marine) who is considered by many to be a marine diesel engine guru/expert, calls these types of elbows and exhaust systems “doomed to fail”.  As you can see, the elbow in the photo is “double jacketed” or 2 walled with the saltwater injected into the elbow right outside and above the turbo outlet. When (not if) the elbow fails by rusting through (hot saltwater will corrode even “stainless”) over time, then this saltwater can be ingested by your turbo or even your engine. On top of that, if the boat is improperly lifted at haulout, water can run back into the turbo fairly easily (bow down a bit). In the case of this elbow, gravity is not your friend!! Tony has written some great articles on boat exhausts and they are available for free on his site (sbmar.com) under “Tony’s Tips”.

    My “old” exhaust elbow (of the type in your photo) did “start” to fail. I had installed an exhaust hose overheat alarm that warned me in time of the impending doom. My elbow, even on close inspection off engine, “looked OK” showing no signs of leaks. However, after I sent it to the radiator shop for a good “clean up”, the pin hole leaks that had developed were evident. I caught it “just in time”., but would never have known without my alarm!!!!!

    Kelly Britz, another NT 37 owner alerted me to Tony and the info regarding these elbows, and the best solution, as well as a local company (National Marine Exhaust in Marysville) that can make a “custom” exhaust for about the same price as these elbows.  Kelly has a full article on sentoa.org describing all of this.

    David, I am sorry to be the bearer of bad news, and suggest that you keep a very careful eye on this elbow as well as ensure that your boat is never lifted with the bow down AT ALL. I wish you had seen my earlier article (post) before making this “repair”.

    I also strongly suggest that you add an exhaust overheat alarm from the Borel company (https://www.borelmfg.com/products/) to possibly provide an “earlier” warning of an internal leak.

    All the best,

    Tom Easterbrook

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