Your manifolds are clogged and toast- see my post below..
JR


Inno wrote:

After having my waterpump and prop replaced over the winter I took my
99 Larson out for a test-drive. It ran great for about 45 minutes
then I started to smell burning rubber. Checking the engine
compartment the rubber bellows that go from the exhaust riser out the
back on one side were melted and leaking a mix of exhaust and steam.
The other side was fine. The engine was not overheating at all.

I am assuming that there was some blockage that prevented sufficient
cooling water from mixing with the hot exhaust.

Any advice on where the restriction is likely to be? This is a 99
Volvo Penta engine with about 250 hours on it, runs very well overall.

I have been advised to take off the exhaust riser on the bad side to
replace or clean out. Is this where there might be some rust or scale
buildup? Anything else that is easy to check?

I drove the boat a short distance again a few days later and there
seemed to be lots of water leaking out of the burnt bellows but no
more melting, but maybe things did get hot enough in 10 minutes of
running it. Could the blockage have cleared itself?

I am very far from the nearest service facility so would like to
tackle this myself. Any advice would be much appreciated.

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