ODD Fan Causing Problems

Did you ever try an SMC reset?

http://support.apple.com/kb/HT3964

With the ODD fan on normal you need to check for overheating.

Get iStat Pro to check the temps.

http://www.macupdate.com/app/mac/20364/istat-pro

Look through the Console logs for anything with "temperature."

May be a faulty ODD temp sensor. Run the hardware test in extended.

http://support.apple.com/kb/ht1509

Running any of the iMac's internal fans at full speed is NOT good and maybe the issue is something is overheating. It maybe that your optical drive is on its way to failing.

The other issue of running any of the fans at full RPMs is that you maybe sucking in more dust, lint and dirt into your iMac by running the fan at full speed. This will cause your iMac to start heating up more and overheating as you are staring to block up the iMac internally with more crud. Also, a fan running at sustained full speeds may result in premature burn out of the fan motor.

If you are doing this, there is another underlying issue going with your iMac. This is what may need to get resolved/repaired.

Your most recent post isn't showing, but these from the email notification are fine, except maybe the CPU, which is a bit on the high side. What were you running when you got this somewhat high CPU temp? And for the ODD temp of 37C the fan was on the normal, default speed?

(All Centigrade)

HD: Macintosh: 39

CPU: 61

Ambient: 26

GPU Diode: 42

GPU Heatsink: 42

Mem Controller: 47

Optical Drive: 37

Power supply 2: 52

See if you can run Rember to test the RAM. Might need to run several loops. Doesn't appear to be locking up because of temperature. But very strange that if you run the ODD fan on high it doesn't, since the ODD temp is quite normal. Can you open up Console in Utilities and look at All Messages, Console and system log for any messages around the time of the freeze? Just post those that might be related from around the time of the freeze and just after when you rebooted.

http://www.kelleycomputing.net/rember/

Message was edited by: WZZZ

Disregard, I now see that WZZZ already suggested the Apple Hardware Test....