I have a system similar to what you are describing in my Rocket.
A 3 lb Safecraft bottle with distribution nozzles at the fuel servo, and at the front of the plenum, with exit ports to either side (like a T). I have a thermal snap action switches located adjacent to the distribution spider, and in the middle of the lower cross tube (between Lord mount cups). These switches are connected to LED's in the panel and to an audio source. Their purpose is to "advise" me that I have a heat condition in either (or both) of those areas above my self imposed baseline (approx. 500*F).
In order to determine whether I have a "false positive" or an authenticated out of limit condition I also have a thermocouple at each location whose real time temp is read through my engine management system. (As an added benefit, these temps can help evaluate the efficiency of your cooling system, as the delta T between them is an indication of the heat being carried away from the air passing through the cylinder cooling fins. I typically see between 60 & 65*F difference between the top and bottom readings.)
My POH for a validated warning is to: 1. Shut off fuel 2. Get the airplane into a nose high attitude to bleed off speed (don't want to discharge the bottle with 170 kt air going through the cowl) 3. Tip the airplane onto the starboard wing at a 30* angle prior to discharge. (My bottle had to be mounted (more or less) vertical because of space considerations - and the install directions call for 30* nose down at the discharge end.) 4. Remove the "safety" pin 5. Discharge bottle.
This system is like insurance, you may want to buy it, but you hope like **** that you never have to use it.
Take the above for what it's worth to you.
David Howe
HR II - Just turned 1000 hours
