Question: I am just beginning to close up my boat for the winter and was looking around in my engine room. I saw a wire going to what looks like some sort of fitting screwed into the side of the muffler on my engine’s exhaust system. What’s going on here?
Answer: I’m really glad to see your boat builder did this. What you are looking at is an often overlooked ABYC requirement for marine exhaust systems. ABYC Standard P-1 (Exhaust Systems) requires a means to sense exhaust system temperature and to provide a warning at the helm on your boat if the exhaust system temperature gets too hot.
Since the exhaust system on most boats is water-cooled, this sensor will respond if the water flow through the exhaust system stops for whatever reason. This is a very important safety feature, because there have been quite a few instances over the years where the water flow stopped due to a restricted raw water inlet or failed raw water pump impeller. In several cases, the exhaust system got so hot it actually melted the rubber hoses in the exhaust piping to the point where they became disconnected.
Once that happens, if the engine is still running you are now filling the inside of the boat with poisonous gas. Also, if the disconnect is close to the engine, the possibility of starting a serious fire on board your boat exists. That simple electrical sensor on your exhaust could be a real life saver.