IMac: Cooling and Harddrive Questions

Question

I have a 2010 21.5" iMac with a Hitachi drive.
I've always had an issue where the fans would, on occasion, ramp up and stay ramped up. The solution for this was always to turn the mac off, and turn it back on. The fans would not, no matter how long the mac was left alone, ramp back down.
Yesterday I replaced the stock Hitachi drive with a 2TB Hitachi drive. Installation went real well. The fans didn't ramp up until a prolonged period of heavy, heavy hard drive access (i.e. partitioning drive, recovering the system from my backup drive to the new drive, copying miscellaneous data from other external drives to the new drive...easily an hour of heavy use).
Curious, I left the system alone for the night with the fans ramped up. The next morning, they were still ramped up. This lead me at this point to assume a few possibilities:
1) The mac, once it gets hot enough to cause the fans to ramp up, has no mechanism for saying "Hey...everything's cool now...you can slow back down!"
2) The mac gets hot, and never gets cool enough for the fans to ramp back down. It seems to me that this shouldn't be the case especially in a situation where its not being used for a prolong period and goes into sleep mode...unless something is preventing it from going to sleep. I'm wondering if something is preventing the drive from powering down during sleep mode.
I'm guessing number two, because the next morning after doing the shut down/turn on that I've done so many times in the past, the fans stayed low for a while (maybe 30 minutes) then ramped back up again. This leads me to believe the system was still running hot.
My next step is going to be to clean the dust out of the system real good and look at istat/istatpro and smcfancontrol. I'm thinking that the minimum fan speed should possibly be higher. Can anyone suggest recommended heat ranges I should be looking at?
Also, are there any aftermarket solutions or fan replacements that anyone has experimented with?
Message was edited by: CMRLunatic

Answer 1

(CMRLunatic: unless you can cleanly remove it leaving not a trace, by installing your own after market fan, you have probably jeopardized your warranty. And, if you drill through the back, your warranty is definitely toast.)
rkaufmann87 wrote: Also I hope you did some research into which HD's work properly in your iMac. I believe the 2010 & 2011 machine need HD's that have integrated heat sensors in them. Prior to 2010 the HD's Apple put in iMacs used an external heat sensor held on by glue.
Roger, just to get this out here for general information. From OWC:
Fortunately, you can reuse the cable that came with your iMac as long as you replace the drive with another model from the same manufacturer we have confirmed works properly with this thermal sensor cable.
That means, in order to upgrade the internal drive, you need to have a connector cable that’s compatible with the brand of drive that you’re installing… and that’s an Apple service part not generally available to the end user.
http://blog.macsales.com/2751-proprietary-cable-can-put-the-brakes-on-upgrading- late-09-imacs
Looks like some of the cables are available here
Interestingly, I changed the drive in my old G3 some years ago from the original Maxtor 10GB to a Seagate 160GB. The Maxtor had no external sensor (it may have had a built-in sensor; I never checked,) but the Seagate has a built-in sensor. And connected through the original data cable, it is showing a temp readout -- the only sensor reading of any kind on the G3. It seems many, if not most, drives have a built-in sensor.