The Borel alarm triggers at 165F. Wet exhaust temp alarms are required for ABYC compliance, but more importantly I have found them to be far an away the very best means of preventing engine overheating. For example, and this has occurred to clients of mine on multiple occasions, if you clean the strainer and forget to reopen the seacock, your engine will overheat, if you are running slowly it could take some time. If you are running under heavier load, if if the engine overheats quickly, the likelihood of having toasted the wet exhaust system, not to mention the impeller, is high. In an extreme case you could end up with an engine room full of soot and even a fire.
However, with a wet exhaust alarm like the Borel, it will sound in 30 seconds or less, long before any damage is done, and in every case I am aware of even before the impeller is damaged. IMO it is far more reliable than a water flow alarm for two reasons. One, flow alarms, because they operate in seawater, are notorious for getting stuck. Two, if the hose between the heat exchanger and the exhaust elbow parts (I've seen this happen on at least two occasions), the engine will not overheat, and the flow alarm will not sound, water is still flowing, to the engine, just not to the exhaust. With an exhaust temp alarm, you are covered for all of these eventualities. The strap to the hose sensor is the height of simplicity as well, some systems actually require you to drill a hole in the hose to install a sensor. The customizability is also a value added for the Borel, I've included water in fuel sensor alarms into the Borel panel, and being able to use one panel for two engines is also a very nice space-saving feature.
I have no connection with Borel, I've simply used their products for many years and have been very pleased. I cover the subject here https://stevedmarineconsulting.com/onboard-alarms-part-i/
However, with a wet exhaust alarm like the Borel, it will sound in 30 seconds or less, long before any damage is done, and in every case I am aware of even before the impeller is damaged. IMO it is far more reliable than a water flow alarm for two reasons. One, flow alarms, because they operate in seawater, are notorious for getting stuck. Two, if the hose between the heat exchanger and the exhaust elbow parts (I've seen this happen on at least two occasions), the engine will not overheat, and the flow alarm will not sound, water is still flowing, to the engine, just not to the exhaust. With an exhaust temp alarm, you are covered for all of these eventualities. The strap to the hose sensor is the height of simplicity as well, some systems actually require you to drill a hole in the hose to install a sensor. The customizability is also a value added for the Borel, I've included water in fuel sensor alarms into the Borel panel, and being able to use one panel for two engines is also a very nice space-saving feature.
I have no connection with Borel, I've simply used their products for many years and have been very pleased. I cover the subject here https://stevedmarineconsulting.com/onboard-alarms-part-i/