One easy way to have an alarm, especially on smaller diesels like many sailboats have, is to clamp a "snap disc" thermostat on the exhaust elbow
. Just wire it to 12V and to an alarm buzzer. They are available in different break temperatures. I've used 185-200 F in the past. If water stops flowing to your exhaust
, your metal mixing elbow
gets hot, the snap disc shuts grounding the wire, this sets off your alarm buzzer. Very inexensive. Available at Graingers and probably Mcmaster Carr. I think they are available in adjustable ones also.
For the bigger diesel
crowd, good idea to have exhaust temp gauges. When a diesel
engine manufacturer certifies an engine installation
, they want to evaluate exhaust temperature.