THE RIGHT STUFF

Exhaust Alarm

Unless you have a dry- stack exhaust, your engine needs a steady flow of seawater to maintain its temperature. Sometimes the flow decreases gradually, due to a failing impeller or the accumulation of debris in the heat exchanger. Other times, the flow might stop suddenly if, for example, a plastic bag suddenly blocks the external strainer. In either case, the high water temperature alarm will sound once the engine’s internal coolant has reached the alarm threshold. By the time that happens, the engine will have already overheated.

After passing through the various heat exchange devices (see Troubleshooter in this issue), seawater dumps into the exhaust elbow where it mixes with and cools the exhaust gas, cooling the exhaust line, and making it possible to use hose instead of insulated pipe to remove the gas (and the seawater) from your boat. Due to the higher operating temperature, any loss of seawater flow will cause an immediate temperature increase inside this elbow. Placing a temperature sender in the elbow, as shown on this Selene, will provide an earlier warning of a problem with the seawater flow because the temperature will increase here more quickly than in the internal cooling system. The earlier warning may allow you to shut down the engine before it overheats, avoiding any damage to the engine or related components. This sensor not only gives you an earlier warning, it also provides a backup to the coolant alarm, and therefore qualifies as the Right Stuff.

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