Why Exhaust Bellows Adhesive? Newbie question.

[joe_nj]

I've been reading the posts about exhaust bellows. Some say if there are small holes leave it alone. More commonly, there's the possibility of replacing the bellows with a tube although I agreed with the post that said if Merc went back to bellows from tube, it's a good idea to avoid the tube.

I thought that the exhaust was going out the exhaust ports on the top of the gunwales.

It dawned on me that if fumes can come out through the exhaust bellows then water can go in. The water then must go up to the waterline level so does that mean when I'm on the bay that there's salt water in my exhaust system? Isn't that doing damage?

Since I'm about to install the exhaust bellows aft end, (and already have it on as a test without adhesive to make sure I can do it), why should I put adhesive on it?

 

[Don S]

Re: Why Exhaust Bellows Adhesive? Newbie question.

I thought that the exhaust was going out the exhaust ports on the top of the gunwales.

Those are the intake and exhaust air for your bilge blower, not the engine. They keep the fumes out of the engine compartment and circulate outside air into the engine compartment.

Your exhaust bellows, Y pipe and at least part of the exhaust manifolds have water in them when running, that's what cools the exhaust.

More commonly, there's the possibility of replacing the bellows with a tube although I agreed with the post that said if Merc went back to bellows from tube, it's a good idea to avoid the tube.

Merc only recommends using the tube on the big block engines only, and that was only for relieving excess back pressure from the exhaust created by the outdrive.
Only the DIYers made it a common thing to use the tube on Alpha drives and smaller engines. Merc started selling kit with the tube because customers wanted them. The only reason DITers use the tube is because it's easier to install. No special tool required.
It doesn't hurt anything, little noisier, but that's it.

 

[joe_nj]

Re: Why Exhaust Bellows Adhesive? Newbie question.

Those are the intake and exhaust air for your bilge blower, not the engine. They keep the fumes out of the engine compartment and circulate outside air into the engine compartment.

Your exhaust bellows, Y pipe and at least part of the exhaust manifolds have water in them when running, that's what cools the exhaust.



Merc only recommends using the tube on the big block engines only, and that was only for relieving excess back pressure from the exhaust created by the outdrive.
Only the DIYers made it a common thing to use the tube on Alpha drives and smaller engines. Merc started selling kit with the tube because customers wanted them. The only reason DITers use the tube is because it's easier to install. No special tool required.
It doesn't hurt anything, little noisier, but that's it.

Thanks for explaining that. I learned something useful today.

I'm still pondering whether to put adhesive on the exhaust bellows aft side.

 

[tpenfield]

Re: Why Exhaust Bellows Adhesive? Newbie question.

Hello Joe,

Keep in mind that your exhaust manifolds have a flow of sea water in the outter jackets of them to cool the system and the actual exhaust, as Don stated. The water mixes with the exhaust upon leaving the elbow piece, which is on top of the exhaust manifold. As you look at your exhaust system, the large rubber coupler piece is where the sea water and the exhaust is mixing and then heading down to the bottom of the transon to go out and through the exhaust bellow/tube.

You are correct, that if your boat is in the water with the engine off, the water level rises inside the exhaust system to a point equal to the outside water level. Careful design and installation consideration are given to this issue so that the water does not easily go so high as to reach the exhaust elbow. In fact it should stay well below it. There are also exhaust shutters within the exhaust system that further prevent water from flowing up into the exhaust system.

whether you are out in the bay or sitting at the dock or where ever, with the engine off, the water level inside the system rises to a point equal to the outside water level.

You probably want to review your exhaust system and bilge blower systems to a greater extent, as it is good to understand how they are supposed to work and be able to spot problems early on.

Folks with thru-hull exhaust don't have the all complexities of a standard exhaust system, but there are still limitations and precautions with those systems.

as far as the adhesive for the exhaust bellows . . . Any reason why you would not want to use it?

 

[Bondo]

Re: Why Exhaust Bellows Adhesive? Newbie question.

Thanks for explaining that. I learned something useful today.

I'm still pondering whether to put adhesive on the exhaust bellows aft side.

Ayuh,... If ya Don't, they have a tendency to pop off when trimmed fully Up...

It's not for water-proofin', but to Keep it there....