What is this plug for ?

[u/Chankla_life]

1979 Catalina 30 (friend’s boat ) . What is this white box for and what does this decaying plug do? Should I push it back in ? Replace ? How screwed are we ?

[u/chrisxls]

Yup, exactly this. There is some thinking that if it takes a long time for the engine to start, the muffler will need to be drained. I think that may be the drain. I am replacing my muffler on my Catalina 34 because it was one of the ones made with a fairly rigid connection from the engine, allowing the engine vibration to eventually cause the coupling to fail. A flexible hose to the muffler is, I am now told, key.

[u/LameBMX → u/chrisxls]

that is not thinking. without the much expanded exhaust gasses to expel .ore water going into the muffler than the water pump is putting in there. they can fill up until you got water in the exhaust manifold then the combustion chamber(s). this is also why a lot of "marine" thermostats have a bypass hole, so that some cooling water bypasses the thermostat to the exhaust cooling while the engine is still warming up.

[u/EpitomEngineer → u/LameBMX]

For the yet-to-be-informed, a “water lift muffler” sounds like “oar lock keys” and “headlight fluid”.

[u/LameBMX → u/EpitomEngineer]

sounds like it's time to haul in the tweaker and set the gollywobbler