... where he talks about engine oil & overheat alarms. His example of the Borel exhaust temperature alarm possibly saving an engine, and at least an impeller, is exactly what happened to me a year ago. I have the Borel Raw Water Alarm, the sensor mounted on the exhaust hose just aft of the engine. We were motoring down the ICW, without a mast (being painted), in traffic, and of course in a sensitive spot approaching a draw bridge 100 yards away, fortunately with no current, when I heard a bang from down below. The Alt belt broke. Within a couple minutes, the Borel alarm sounded and we shut off the engine. There's no need for any visual notification with the Borel, that thing is LOUD. The point here is, and confirmed by Steve in his article, our engine coolant alarm / "buzzer" never went off. When we got to where we were going, I checked the water pump impeller and it looked like new, no cracks, no stress, there was no need to replace it (I did anyhow, it was a couple years old). I was anticipating some damage but found none, I wasn't looking forward to flushing out the heat exchanger of rubber bits. And I'm confident the engine survived just fine and didn't miss a beat. Had it not been for the Borel alarm, given the situation, I bet I would have pushed it until the coolant buzzer went off, and I bet there would have been consequences.

I think I've tested the alarm once or twice using a heat gun, waving it back & forth on the sensor.

Cheers, John