I had my AUX loop pump in my rig fail before I finally ripped it out and I managed to limp along for a few months running 100% passive on that loop. It mainly cooled the northbridge, mosfets, and a few other random non critical things, but I had a temperature probe on the northbridge. It would spike around 70c, and then the temperature would start dropping (rapidly at that) as the coolant started to move. Only prob;em was I was leaking coolent BAD (failed oring, lead to pump death, ect) but didnt have time to tear into it and replace every thing, so I would have to top the coolent off and bleed the thing by just tilting the computer... I've literally had boiling coolent in my loop when the water ran low on the nortbridge....