exhaust cooling question....

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gb387

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To make a long story short... After safely retuning to shore on one engine and finding a pump full of wood debris... the exhaust temp alarm sounded on that engine and I would like to know a bit more on the path the water takes, I was concerned there was more damage beyond the debris ingestion. I cleaned the pump out, rest the code and returned to the lake with no issues. I'm just don't understand the path the water takes in and out of the exhaust and would like to know more.... Thanks!
 
Post #4 HERE shows the flow of water through the 4Tec exhaust. Post #15 has a link to a video from a similar post where they explain it as well.

Water comes into the front of the exhaust manifold from the pump. Goes through the manifold and exits in 2 places. Top exit goes coupling and hose to muffler, 2nd exit goes out through flush port.
 
That does help alot, I see the intercooler complicates the system slightly but still easy to understand. What is not quite answered is how does the water actually forced into the boat? Is it forced in through the rotation of the impeller/pump pressure? I know there's no way it would enter through the garden hose connection, to me it looks as if the water is traveling through the system backwards when you are using a garden hose connection is this correct?
 
That does help alot, I see the intercooler complicates the system slightly but still easy to understand. What is not quite answered is how does the water actually forced into the boat? Is it forced in through the rotation of the impeller/pump pressure? I know there's no way it would enter through the garden hose connection, to me it looks as if the water is traveling through the system backwards when you are using a garden hose connection is this correct?

Yes, the water is entering backwards through the hose connection. The water is coming from the pump (through some channels in the pump I assume) and then flows up to the exhaust manifold. Hence the reason you need to keep tow speeds below 12 mph, so as not to force water into the exhaust causing it to back-fill and flood your motor.
 
Excellent, thank you!! Now that I understand how it works I also understand why we had the condition we had should it ever occur again I will know what's happening.
 
One last thing... Does a exhaust manifold have a water jacket type setup? And the muffler water actually enters the muffler itself and not contained in a water jacket... Is this correct?
 
Think of the exhaust manifold as a cooled exhaust pipe. The hot exhaust gasses exit the combustion chamber through the exhaust manifold. The gases then flow through some exhaust tubes/hoses into the muffler, then out the rear of the boat.

These hot exhaust gases are heating up the exhaust manifold metal and must be cooled in order to prevent things from melting, that's where the cooling water comes in. The manifold is jacketed in that the source water is pump into an outer sleeve/jacket within the manifold to help cool it. The exhaust gases do not mix with any of the cooling water in the actual manifold, that happens a bit further downstream.

Does this help?
 
It does, just trying to get a full understanding... Something I have always miss understood. It was bothering me why I was getting a high exhaust temp warning but I now understand how it can happen. Thanks for the help!!!
 
Water does not flow IN through the hose connection when you are on the water. The hose connection becomes one of the outlets for the water, not an inlet. Water is forced up to the manifold via holes in the pump housing just past the impeller. The same pressure that created forward thrust out the nozzle pushes some of that water back to the exhaust manifold.

This is how, when you are flushing, you see water coming out of the pump since the path is reversed. It also explains why you got the exhaust temp warning, as the blockage was causing cavitation, which reduced your pump pressure dramatically, which mean that no water was getting forced up to the exhaust system.

Hope this helps.
 
Water does not flow IN through the hose connection when you are on the water. The hose connection becomes one of the outlets for the water, not an inlet. Water is forced up to the manifold via holes in the pump housing just past the impeller. The same pressure that created forward thrust out the nozzle pushes some of that water back to the exhaust manifold.

This is how, when you are flushing, you see water coming out of the pump since the path is reversed. It also explains why you got the exhaust temp warning, as the blockage was causing cavitation, which reduced your pump pressure dramatically, which mean that no water was getting forced up to the exhaust system.

Hope this helps.

I was answering 2 questions with my reply (post #4). but I could see how it could be misleading. He asked if the water is traveling backwards when on the hose, which is what I answered in my 1st sentence. Then I went on to answer his 1st question about how the water gets from the pump to the manifold due to pump pressure.
 
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