1989 5.7 Mercuiser exhaust plugged

[Dalbery]

I just bought a Glastron Futura 205SL. It is very clean and has been garaged it's whole life. The guy I bought it from says That at the end of last seaon, last time he took it out that it got really hot under load and that the starboard exhaust manifold is what is really getting hot. So I believe the water blockage is there. I know these commonly break down with age and is a fairly common issue. He did replace the water pumps with no change in the heat.
My question is, normally does only the riser go bad or should I replace the exhaust manifold and riser? Luckily this boat is designed with a lot of room around the engine and it looks like I can get to everything fairly easily. Are there any tips or tricks to removing the manifold? Thank in advance.

 

[Scott06]

Remove the risers from the manifolds and inspect the water passages. not sure the year but if used in salt or brackish and they are 5 + years old likely they will need replacement . Drain the manifold before you take the riser off

 

[Dalbery]

Remove the risers from the manifolds and inspect the water passages. not sure the year but if used in salt or brackish and they are 5 + years old likely they will need replacement . Drain the manifold before you take the riser off

This boat has never seen saltwater or brackish, so I'm assuming they're probably still the original manifolds. The engine and engine compartment still look like brand new though.

 

[tpenfield]

Both manifolds and risers can get clogged up, so they both need to be checked - fixed - replaced.

 

[Scott06]

This boat has never seen saltwater or brackish, so I'm assuming they're probably still the original manifolds. The engine and engine compartment still look like brand new though.

Freshwater they generally dont corrode, but could have debris in them. Would open to inspect the water passages. Also possible that if the water pump impeller disintegrated there are pieces of it clogging water flow, especially in thermostat housing . folks here can walk you through it.