Slap a temperature sensor on/in/near the heater
Monitor current through the heater for temperature coefficient response
Capacitive sensing of ice on the heater
A timer that shuts off the heater after some time and a buzzer to alert the crew
You could even have a thermal fuse with a manual time-limited override
Honestly there's so many easy ways to prevent thermal runaway that creating a situation where THE ENGINE FALLS OFF is inexcusably negligent.
My space heater has no less than three independent, redundant safeties. As does my clothes iron, my coffee pot, my slow cooker. It really is not that complicated.