Over temp protection?
 

I'm just about finished assembling my watercooling rig, but one thing is still bugging me - o/s independent overheat protection. I already use MBM5, so I can use that to issue a shutdown command, but I'm looking for a failsafe should the software lock up.

Does anyone have any ideas how I could implement something that will turn the system off should the cpu get too hot?

I've been thinking about this problem too, especially considering a friend of mine lost his CPU yesterday due to a generic brand pump dying on him. What you'd want to do is rig up a thermistor by the core of the CPU, run to some circuitry that has the ability to cut the AC power to the ATX power supply in the event that the temperature exceeds an insane temp, like say 80c or so.. Set it as high as possible, so it doesn't accidentally trip anytime except the worst case scenario.. Really wouldn't be too hard to do either.. But if you used a relay, the circuit may need a battery backup to keep the AC cut off after the ATX power supply stops feeding power to your temp monitor, and keeping it from turning back on after the temp goes down might be a hassle too. But not impossible. :)

I see we're thinking alike. :)

I've had a look through the Radio Shack website, and think I've found something suitable - thermal fuses. These go open circuit at a preset temperature. The 72C or 77C ones look like they could work if I connected one in series with the ATX "power good" wire. If I remember this correctly, "power good" needs to be grounded for an ATX power supply to start; Interrupting this wire should shut things down. It wouldn't be a clean shutdown, but I'd much rather reinstall Windows than have to get a new cpu.