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Old 31-01-2021, 22:00   #1
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Threaded exhaust sealant

We have put a new exhaust elbow on. It has a threaded nipple in the middle, and I can hear a little bit of exhaust leaking out.

Whats a good high temp threaded sealant to use?

In NZ we have loctite and permatex readily available - possibly other brands too.


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Old 01-02-2021, 01:43   #2
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Re: Threaded exhaust sealant

Look at car exhaust sealants at auto shops in your area. Exhaust elbow temperature is very modest compared to car exhaust systems.
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Old 01-02-2021, 08:41   #3
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Re: Threaded exhaust sealant

Locktite is really aimed at locking threads more than sealing, and Permatex is more aimed at making gaskets than sealing threads, although either might seal the leak. In either case, make sure that it dries before you apply exhaust pressure.

You might consider teflon tape, which is made for sealing and will let you screw the thread down tightly as well.
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Old 01-02-2021, 08:58   #4
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Re: Threaded exhaust sealant

Most people think of Permatex and Loctite as specific products (as tkeithlu notes) but they are actually both companies with wide ranges of products. For example, Permatex makes threadlockers that are very similar to the "Loctite" that most folks are familiar with, and vice versa.

From my automotive experience (I have no experience with marine diesel but don't see why it would be materially different with regard to exhaust sealant) I like Permatex Ultra Copper RTV for sealing exhaust connections.

Also, my personal preference is to avoid using plumbers tape anywhere. That stuff just seems to cause problems long-term. Much better, IMO, is something like Permatex high-performance thread sealant (56521)
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Old 01-02-2021, 09:13   #5
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Re: Threaded exhaust sealant

I think it's sort of mud and sodium silicate. Put it on threads before screwing together or use it on gaskets. Turns into rock.
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Old 01-02-2021, 10:11   #6
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Re: Threaded exhaust sealant

DO NOT use "teflon tape" DO NOT use any type of RTV, or "gasket maker" or "pipe sealant." This part of your exhaust system is way too hot for these kind of products. This is all very bad advice. Many of these products give off VERY toxic fumes when overheated.

The muffler sealant is one answer, and it will stop the leak, for sure, but you will have a nightmare getting those parts separated in the future.

Use a copper (or copper/nickel) based high temperature anti-sieze. (lots of brands!) It will seal the leak (Assuming you actually have properly mating threads), and give you a fighting chance of getting the threads apart in the future.

You should have some of this on the boat anyway, it is the right thing to use on engine nuts and bolts to be sure you can take them apart next time.
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Old 01-02-2021, 10:24   #7
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Re: Threaded exhaust sealant

Apologies if my reply above wasn't clear enough. I agree 100% on not using teflon tape or thread sealant on exhaust connections. My recommendation on Permatex thread sealer was as a general alternative to teflon tape wherever one might use teflon tape (certainly not on exhaust). The Permatex Ultra Copper RTV is absolutely up to the task of sealing exhaust connections, and will not turn into a rock like some other products.
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