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Andy 240

1996 chaparral 1930 4.3 Mercruiser exhaust bellow buring

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Hi I have A 1996 chaparral 1930 with a 4.3 Mercruiser alpha one I have an issues With the right side (By power steering pump) exhaust bellow burning and melting other side is fine looking for some advice on  is could be thanks .

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Not enough water flow into it ?  Do you idle for 5 minutes or longer ?

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All the exhaust exiting the engine must be quenched with water at the point where it exits the exhaust elbows. This is accomplished by mixing with the raw sea water stream after that water has visited the engine water jackets. Likely you have a blockage in the manifold and/or riser on that side. Find the manifold inlet hose and remove it, then start the engine (in a cold state) for a few short seconds and confirm water feed to the manifold. If it seems normal, then remove the manifold and riser and start a comprehensive internal inspection. These are wear items and on a 1990 raw water cooled engine, you may find rust and sediment has blocked off water flow. Also, if you have cooked the exhaust hoses, you almost certainly have smoked the exhaust flapper valves  located in the exhaust Y-pipe. If the flapper is not in it's normal location, then find it as the rubber hinged valve is made from stainless steel and it will restrict your exhaust flow exiting the transom plate if it has fallen into the abyss.  W

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The age of your boat / engine requires a person like Wingnut to do a checkout of the engine & drive parts.  A lot of us boaters have had to downsize for many reasons.  As a result the boat is last in line for money.  But that does not stop the wearing out of parts. Different previous owners / drivers can brutalize a well cared for boat very quickly. 

 Flipping the boat key to WOT people playing follow the leader in shallow mucky / sandy / weedy water does wonders to wear out all the system parts.  So does running the boat on a trailer with a hose setup.  ": I can hear & feel myself racing ".  As  the engine hits & holds WOT rpms.

Oh well.

Treat your boat like the best girl frend you can remember.    Money & attention were no problem.   Boats are called she. For a good reason.   Enjoy her.    :thl_speedboat:

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I've noticed that one side of my exhaust is a bit warmer than the other on my port engine.  Nothing like what you're experiencing, but similar.  I've assumed that it is the difference in water flow through the two exhaust manifolds(I'm a lowly Mechanical Engineer, so that may be an incorrect assumption).  There is no means to ensure even flow of water between the two sides and water will take the path of least resistance.  I'm contemplating putting a hose clamp on the supply hose on the "cool" side to force more water through the "warm" side.  I've just done the head gaskets on this engine and cleaned the exhaust manifold passages as well as I could, but the flow is no longer balanced(and may have never been, we've only had it out about 6 times so far).  I suspect you have a blockage either in the exhaust manifold, or the supply hose  on the hot side.  Work your way through the system until you find the blockage. I don't believe my boat has flappers(1992 Sig 280 w/431a engines), as the exhaust risers are well above the water line(3" below deck level), so I'll defer on that to Wingnut.

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1 hour ago, JPFunk said:

I've noticed that one side of my exhaust is a bit warmer than the other on my port engine.  Nothing like what you're experiencing, but similar.  I've assumed that it is the difference in water flow through the two exhaust manifolds(I'm a lowly Mechanical Engineer, so that may be an incorrect assumption).  There is no means to ensure even flow of water between the two sides and water will take the path of least resistance.  I'm contemplating putting a hose clamp on the supply hose on the "cool" side to force more water through the "warm" side.  I've just done the head gaskets on this engine and cleaned the exhaust manifold passages as well as I could, but the flow is no longer balanced(and may have never been, we've only had it out about 6 times so far).  I suspect you have a blockage either in the exhaust manifold, or the supply hose  on the hot side.  Work your way through the system until you find the blockage. I don't believe my boat has flappers(1992 Sig 280 w/431a engines), as the exhaust risers are well above the water line(3" below deck level), so I'll defer on that to Wingnut.

Normal for starboard riser to be warmer.  Mine runs 10 deg warmer than the port side.

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My 2002 V8 5.0L  Both run unevenly.  But close enough. Supposedly there is a balancing valve with a spring to help keep both sides close.  I never opened that casting up.

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