We have decided to include a master warning on Ted's IVP for engine fire, JIC.  In order to light up the annunciator we need a ground fault and are trying to figure out the best way to sense the overtemp condition.  I realize that while the situation under the cowl with a water cooled engine is quite a bit different from that which exists in an air-cooled installation, the methodology would probably be very similar in determining that something had gone horribly wrong under the hood and that a fire is the likely culprit causing the elevated temperatures.  With an air-cooled engine, the sensors would undoubtedly be located somewhere outside the baffling, probably back near the firewall and just under the upper cowl, and I can't see anything wrong with looking in the same place in this installation... it seems to me that would be the most likely place for heat buildup to occur, away from the cowl outlets and most of the turbulent airflow, and high in the enclosure.  If any of you have done something along these lines I'd sure like to hear about it.

Not wanting to get overly complicated I thought the most reasonable approach would be to find some sort of temperature sensing device that acted more like a switch than a variable resistor, and would close (or open and trigger) the circuit to the annunciator at some predetermined elevated temperature.  I've located some thermal fuses with a set point of 315deg F and am wondering if that is too low a temperature to sound the alarm, and if so, what temp some of you might recommend.  (It looks like 365deg F is another common value... would that be better?)  I'm assuming the temperatures under the cowl don't typcially get much over 200-250degF, as beyond that we'd probably be damaging the composite structure.

All comments and suggestions gratefully accepted.  TIA.....

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