Which caulking to use for exhaust hoses?

[bwindrope]

I'm in the process of replacing my exhaust riser and to do so will be installing a reducing coupling between it and my muffler. It's a different story as to why I need the coupling, but my question has to do with what sealant/caulking is typically used on exhaust systems?

For anyone interested in the longer story of why and how I am replacing the riser on my Gulf 32, and why a reducing coupling is needed, see my blog at Stories of Aeolus- Our Gulf 32 Pilothouse

That I have been able to disassemble the old stuff makes me think it isn't 5200, but does that mean people use 4200? Or is it polysulfide? All these connections occur after water injection, and so do not reach very high temperatures. I figure one of you out there has an informed opinion...

Opinions?

Thanks

[negrini]

I have used sealant for diesel joint heads. Can't remember composition, but it is very temp resistant. One drawback it is too liquid, almost rubber sealant like, so if you need to patch a larger gap, that certainly will not work. But for hose connections (correct sizes), that's been of my choice. I've used it to seal LPG hoses with very good results too. A little harder to remove if needed.

[sailingdog]

Given that it is an exhaust system, I would definitely use a high-temperature resistant sealant. RTV Silicone comes to mind. If there is any plastic involved, DO NOT USE POLYSULFIDE-based SEALANTS, since they are known to attack many common plastics.

[bubb2]

monkey snot the blue stuff from perm=a=TeX

[sailingdog]

Permatex is the company I was thinking of, thanks Bubb.

[bubb2]

Dog I wish I could spell thank you!

[sailingdog]

LOL. Any time Mike...

[bwindrope]

Thanks y'all. I know permatex would work and be heat resistant, only I know for certain that that is not what has been used before. The old stuff, probably original, was white and had the consistency of 4200. I just had some recent work done at Schooner Creek Boat Works in Portland, OR a few years back and they sealed up the new hoses with a white 4200 like stuff. It is flexible, but pretty firm and yet not impossible to remove.

That is why I was wondering about 4200. Since I already have 4200, I would rather not go out to buy the high temp silicone, which is the Permatex, if what the boatyards are using is what I already have. Again, all these junctions are downstream of the raw water injection and so none of this gets up much above maybe 150 degrees F. I can touch it comfortably during engine operation.

I've searched around on the 3M website and found nothing definitive. I've googled it, and found nothing either. Figure I will call Schooner Creek Boat Works on Monday if I don't answer the mystery of this white 4200 like substance before then.

Thanks for the suggestions...

[halekai36]

Regular old Pipe dope and teflon tape will work fine! They are used in industrial and commercial applications that have SIGNIFICANTLY higher operating temps than do a wet exhaust. It's what NPT fittings are designed to go together with!

I use Teflon tape:

Solubility: Not soluble in water, organic
solvents, acids or bases.
Reactivity: Chemically inert to most chemicals.
Flammability: Non-flammable.
Thickness: 3.0 mils min.
Temperature Use Range: -450°F to 500°F.
Appearance/color/odor: White tape. No odor.

Combined with

Hercules Real-Tuf Pipe Thread Sealant:


A multi-purpose thread sealant formulated with the highest percentage PTFE content on the market. PTFE particles fill cracks and tiny thread imperfections - providing superior lubricating and sealing properties. Leak-free joints can be tested and put into service immediately. Holds tight against vibration, expansion, and contraction. Brushable; non-separating; will not run or drip from joints. Soft set; no cure time required. Withstands temperatures from -50ºF to 500ºF (on steel pipe), and pressures of 12,000 psi (hydraulic), 2600 psi (gas). For use with liquids, including acids and alkalis and gases (except oxygen). For use on metals, including galvanized steel, black iron, aluminum, copper, brass, stainless steel and on PVC, ABS, and CPVC plastics (for use on specific brands of CPVC pipe, verify suitability with pipe manufacturer). Superior anti-galling properties with stainless steel. Excellent resistance to strong acids, alkalis and ketones. Non-flammable and contains no heavy metals or volatile solvents. Certified to ANSI/NSF Standard 61, safe for drinking water lines. Meets Fed. Spec. TT-S-1732. White.


We don't need to over think NPT threaded fittings. Marine sealants are not the right product for the job when .30 cents worth of teflon tape and some pipe dope will be more than sufficient.

P.S. You really ought to consult with the engine manufacturer before reducing the exhaust outlet diameter! It can cause serious problems. If the engine was designed with a 2" inch exhaust reduce it only after confirming it is safe and won't harm the engine!! Disregard this if you already have..

[bubb2]

halekai36, thank you for the big print. being of advanced years you curiosity is welcome. thanks!!!!!!!!!!!!!1