Mhhh BB2K: i now let my pump on 24/24 even when the PC is off. That means, no fan. No coolant over-heating. My water is usually @30°C (i know, sh*tty rad) when running, and at power up i find it @27°C. I've got a 27W pump, in a sealed closed loop.
And no worries of a pump failure, i can hear its humm before turning on the PC. If something is wrong i just don't press the switch
