Why do I/O coolant systems run water out of exhaust manifolds?

[sikemd]

I've recently diagnosed my boat with bad exhaust manifolds when I seen water in my cylinders and I am very curious why the coolant system runs water out of the exhaust manifold when they deteriorate so fast and the end result can be so devastating to the engine, as well as quite costly in a maintenance aspect. Also, as far as I know there is really no way to know the condition of the manifold until they have began to go bad. I really can't understand the thinking behind this, why isn't the water returned via a hose or some other method rather than through the metal exhaust? The only thing I could think of is that the manifolds need cooling as well in order to keep temperatures in the engine bay safe for the boat and air intake. If anyone could clarify this design I would appreciate it. TIA.

 

[Howard Sterndrive]

Re: Why do I/O coolant systems run water out of exhaust manifolds?

The only thing I could think of is that the manifolds need cooling as well in order to keep temperatures in the engine bay safe for the boat and air intake.

You got it.

They routinely last 20+ years in my area (fresh water only) if winterized properly.

 

[Number21]

Re: Why do I/O coolant systems run water out of exhaust manifolds?

The manifold is made out of the same cast iron as your engine. The bare metal inside your engine is also full of water, they must be cooled.

 

[bruceb58]

Re: Why do I/O coolant systems run water out of exhaust manifolds?

Exhaust temperature is around 800?. Imagine what would happen if they weren't water cooled.

In a full closed cooling system, water is run through the manifolds and returned to the heat exchanger. Problem with a system that cools the manifolds as well as the block is that the heat exchanger needs to be sized a lot higher to handle the larger heat load. No matter what system you have, the risers will always have water mixed with the exhaust as it exits to keep that portion of the exhaust system cool. There is really no other good way.

 

[HT32BSX115]

Re: Why do I/O coolant systems run water out of exhaust manifolds?

The only thing I could think of is that the manifolds need cooling as well in order to keep temperatures in the engine bay safe for the boat and air intake.

Howdy,


You hit it exactly! The only boat exhaust systems that do not have water/exhaust mixing at the exit are boats with exposed engines and "dry-stacks".

ALL boats with enclosed engines and exhaust exiting through the hull, side, or through-prop, MUST have water exit with the exhaust to prevent overheats and fire where the exhaust tubing exits the boat.....It not just required because it's safer, it's required by just about all regulatory authorities (Like the USCG and Transport Canada etc.