Sealing exhaust water leak between exhaust hose & muffler

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Veteran Member
Nov 6, 2007
Hi all,

Thought I'd pose a question*to the forum.* I have a 2002 Cummins 6BT5.9M engine in my boat.* Since I've acquired it, she's had a slight exhaust water leak at the point the 6" diameter exhaust hose joins the inlet to the fiberglass*water lift muffler.* This results in a small amount of salt water leakage (perhaps an ounce or two in a day) onto the platform on which my genset is mounted.* Last year, I had to remove the genset housing, grind off the resultant corrosion and repaint it.

The muffler inlet is slightly out-of-round, and this was accentuated by the previous owner who apparently decided the best approach to fix the problem was to simply crank down on the exhaust hose clamp, which crushed the fiberglass inlet slightly.

I've*faired*the inlet,*using West System resin and filler*and then sanding using a hose clamp as a guide to approximate the required radius.**It's better,*but there's still a slight gap.* We're talking perhaps a millimeter, and that's on the top.

Does anyone know of a flexible, moldable, removable filling compound or tape*I could use for this application (hot salt exhaust water and exhaust gas)?* Something I could affix to the muffler and then slide the hose on and tighten?

Any other ideas?
Remove the rubber hose. Inspect and measure both the hose and muffler for any cracks and out of round. This is a big stiff hose and any imperfections on either surface will result in a poor fit - as you now have.* If you have a cracked pipe, throw the muffler away and buy new.*If the muffler pipe is not cracked, call the muffler*manufacturer and ask their opinion. You have two potential safety problems, one can sink the boat and the other can put exhast gasses into the boat.
I think BS has the answer. I have used the red hi temp silicone on industrial engine exhaust flanges and it works great.
Thanks, all.* BornSailor, I like that idea.* I assume you mean this:

By "when it's cold", do you mean appling the Permatex to the*muffler inlet to*fair it, letting it dry, and then assembling it all?* Or applying the Permatex to the muffler inlet and assembling the muffler & hose before the Permatex dries?

Sunchaser, the crack in the muffler is only in the area directly under the hose.* There's no manufacturer info on the*muffler;*it may be custom-made by the yard and I'd like to avoid retrofitting a different type.*
You can get various high temp silicones at your local auto parts supply. The colors indicate the temps they can handle. I've used the black successfully in exhaust applications.
Dear JS,

This suggestion may not be for the faint of heart, but might be a permanent fix.

Get a bronze nipple or hose nipple that will fit your rubber exhaust hose,
Cut off the nipple damaged inlet nipple from your muffler,
Using a hole saw about 1/8 inch smaller than the new nipple threads, cut a co-centric hole in your muffler where the old pipe exited.

Get a piece of high density plastic that is rated for high temps, check out, maybe PTFE, (maybe try stock nummber 45450) and cut a plate that is larger than your new bronze nipple, large enuf to allow room to bolt this right to your muffler, around the edges of the plate.

Maybe there is a plastics expert out there who can help.

Cut a hole the perfect size to thread,(tap) your new bronze nipple into this plate.

Now I don't see where you said if the muffler is square or round. If the entrance side is flat that makes things easier. If curved you will have to shape the back of the plate to lay against the curved face of the muffler.

Once you have the plate all shaped and fit, clamp it over the old bored out hole. The hole in the muffle should still be too small.

Drill and bolt this plate to the muffler using high temp gasket maker. Don't skimp on bolts. I would use Stainless and large washers, spreading the load. It may be a bugger to get the nuts on the inside of the tanks, so either get extras, or use sheet metal screws, tightening carefully, use lots, also SS.

Once the plate is bolted you can re drill the hole, making the hole in the muffler the proper size.

(the undersized hole just might have made it easier to line the plate up for bolting, but I think its important to get the nipple threads to catch both the plate and the original muffler)

Screw in the new nipple and go cruising!

But first, send me the left over PTFE so I can fix my muffler!

Come to think of it, if your muffler has flat sides, you could just bolt on a floor flange and save a lot of trouble.

Comments welcome. Work in progress.
Thanks for the suggestion, Capt. Dan.* You're right about that not being for the faint-of-heart.* There are a few complicating factors.* My muffler is a vertical cylinder, with a round 6" (approx) inlet and a similar-sized round outlet.* The entire muffler is constructed of FRP.* Not only does the curved and not completely smooth surface make for an interesting study in backing plate construction (as you suggest), but the 6" diameter of the inlet would require the use of some sizable taps to cut threads.* Might be difficult to do well with a mechanical*means (milling machine?).

Building on your suggestion, an alternate approach would be to cut off the damaged inlet, acquire a FRP tube that fits into the muffler inlet hole and then glass*it all together.* It would obviously be easier to cut off only the end of the damaged inlet tube*(rather than the whole thing),*get a FRP tube that fit tightly inside the remainder of the inlet tube and glass it in.**However, the OD of a tube that fit inside the inlet tube would be too small for the existing exhaust hose.

Given the*magnitude of these approaches, I think I'll try the high-temp silicone approach first.

Happy sailing!

-- Edited by jethrobd on Friday 2nd of April 2010 11:35:32 AM
All too often these types of issues result from a moving engine ( normal or abnormal) and a fixed mount FRP "box."* As the hose moves and the box doesn't, problems arise. Have you watched this area as the engine goes from idle to full RPM to insure movement of the hose is restrained at a FIXED point other than the weak area - the inlet*tube?

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