Q: iMac gets very hot, and even is warm when idle...

Please post the EtreCheck output

<https://discussions.apple.com/docs/DOC-6174> or <http://etrecheck.com>

It could be many things.  Adware using your iMac to generate money making "Clicks".  Anti-virus package doing lots of busy work.  A Mac cleaner app working against you.  Accumulated dust inside.  A disk drive failing.  The EtreCheck output may help identify some issues.

In addition to Bob's suggestion, try a SMC reset. The article covers when this is required, but doing this will not affect anything.

Reset SMC

I do not see anything in your Etrecheck report that would be causing your excessive heat issues.

What can reduced the longevity of ANY computer and newer aluminum designed iMacs is basically too much internal or more than reasonable or excessive exposure to high internal temperatures.

Heat is the enemy of any electronics and, especially, micro electronics.

Apple designed a thin enclosure that, in reality, acts more  like a portable oven or toaster that is basically "slow roasting", over time, the iMac's inner components. The rear of the iMac has been stated in various Apple conversations to act as a component to "draw away" or convect heat out of the inside of an iMac.

While some of this is true, in theory, the reality is the whole iMac box structure is all aluminum. Aluminum is a serious heat conductor/absorber, but has some ability to conduct its heat out from the material, as well.

Unfortunately, the iMac's internal components generate more heat than the aluminum enclosure can conduct away and to the outside of the iMac.

There were never enough internal fans nor these fans spinning fast enough to keep an iMac, relatively, cool on the inside.

If the inside of the iMac fills up with dust and/or dirt particles and lint, the internal heat factor goes up considerably.

Once a year, I use a vacuum to vacuum ALL of my 2009 iMac's vents, slots, the various connection ports, the optical drive slot and the bottom air intakes and I remove the RAM module area metal cover and lightly vaccum inside of there. Basically trying to suck out as much loose dust, dirt and lint particles as possible.

Unplug from power and disconnect everything from your iMac, first, before doing this.

Lay the iMac screen down on a soft toweling set down on a hard, stable surface before doing the vacuuming procedure.

I use the vacuum crevice attachment to very lightly move along my iMac so as not to both scratch or damage the outside finish and DO NOT USE ANY BRUSH attachments to cause any type of electrostatic discharge on anything on my iMac.

STAY AWAY FROM USING CANS OF COMPRESSED AIR, PERIOD!

This will only make the accumulated dust, dirt and lint situation worse!

Another thing I do to keep heat down is run a software fan control app to ramp up the iMac's internal fans to keep internal temps down.

The trick is to keep the fans running a little faster than what Apple has set, by default from the factory, but keep the fan speeds from being too fast so the fans act like internal vaccuums sucking into your iMac much more outside dust, dirt and lint particles at a much faster rate.

I, typically set my iMac's fans bewtween 1400-1700 RPMs and find that this is an acceptable increase.

I, also, use a small footprint, portable desktop fan that blows cool air around the hottest area of my iMac, typically the upper left rear of my iMac ( when facing the iMac's screen).

When really working my iMac doing illustration work, the temp of the CPU will rarely peak over 110° F and the hard drive temp is around 110° F and the GPU (which is one the hottest components in an iMac) I never let get hotter than 130° F.

Keeping your computer as cool as practically possible is what is going to keep it running well longer.

Hi Bob, sorry for the late response. I purchased a hard drive to clone my iMac before I started tinkering, and made a new back up too. So here is my etrecheck report, I hope you can work out what is going on. Thank you.

Backups are Good and always encouraged.

I also do not see any of the more common 3rd party software trouble makers.  So what I'm going to call out are just oddities that may not be a problem.

   12 GB RAM

        BANK 0/DIMM0

            2 GB DDR3 1333 MHz ok

        BANK 1/DIMM0

            8 GB DDR3 1333 MHz ok

        BANK 0/DIMM1

            Empty  

        BANK 1/DIMM1

            2 GB DDR3 1333 MHz ok

You have 3rd party RAM installed.  That is not a problem, although your configuration is a bit odd.

You generally want to have matched pairs in the DIMM0 slot, and when using the DIMM1 slots also have matched pairs.

The iMac can deal with your configuration, but if the same sized RAM in in bank 0 & 1 of DIMM0, then the iMac will alternate memory access between the 2 RAM cards, giving a slight speed up in memory access.  Reading RAM causes the electrons stored at a giving address to be drained to determine their value.  Then the RAM must recharge the location to put that original value back.  Interleaving matched pairs, allows the chips in one RAM card to do the re-charging while the the other RAM card is being read.

The configuration you have at the moment means the iMac cannot interleave access, so it has to wait for the re-charge cycle to complete before it can read the next memory cell.

You should really put the 2GB cards in the same DIMM0 or DIMM1 banks so you at least get interleaved access with 4GB of your RAM.  Since you do not have a 2nd 8GB RAM card, you cannot do anything with that but let it wait for the re-charge cycle anytime it is accessed.  You could get another 8GB RAM card of course

But because you do have 3rd party RAM installed, I am going to suggest you run "Rember" overnight to make sure your RAM is behaving properly

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

Set Loops: [X] Maximum

and run overnight

I suggest you quit a many apps and background processes as you can, so that Rember has the maximum amount of Free RAM to test.

    Sep 5, 2016, 09:03:50 PM    ~/Library/Logs/DiagnosticReports/com.apple.dock.extra_2016-09-05-210350_[redact ed].crash

    Sep 5, 2016, 09:03:37 PM    ~/Library/Logs/DiagnosticReports/com.apple.dock.extra_2016-09-05-210337_[redact ed].crash

    Sep 5, 2016, 09:03:02 PM    ~/Library/Logs/DiagnosticReports/com.apple.dock.extra_2016-09-05-210302_[redact ed].crash

The com.apple.dock.extra process seems to keep crashing, sometimes back-to-back.  This is a bit annoying.  Unfortunately I do not know much about com.apple.dock.extra, and cannot give you any advice about why.

Google "com.apple.dock.extra crash" and maybe someone else has solved this and you can use their solution.

Based on the time stamps, I do not think this is happening enough to cause your problems, but then again, I'm not sure what your base problem is so I'm pointing out oddities.

    [running]    com.WesternDigital.WDSmartWareD.plist (2012-06-14) [Support]

    [running]    com.wdc.WDDMservice.plist (2012-06-14) [Support]

Do you know what this is?  Generally Western Digital is associated with a storage device.  In general Macs do not need any extra software to access a disk drive.  If this software is doing something special and you want/need it, then OK.  But if it is not needed, then I suggest removing it.

    [loaded]    com.facebook.videochat.[redacted].plist (2014-08-09)

I want to be careful here, as this comment it total FUD (Fear, Uncertainty, and Doubt), but Facebook has not always cared about how much resources they use on your devices.  The reason I say FUD, is because I do not know much about Facebook Video Chat service, and do not know how resource intensive it is.

You might want to boot into Safe mode, assuming you can stand to run in a minimal environment, and see if the system exhibits the same behavior

<http://support.apple.com/kb/ht1564>

Safe mode will not load any of the 3rd party additions listed, and if things work better, then that would point to one of the 3rd party additions.  NOTE: Safe mode is really just an experiment, as it is not the normal operating mode, and OS X uses some less optimized drivers for things like the display, but it is a great test tool.

The last thing I'm going to suggest, is that you may want to make a Genius Bar appointment at an Apple store and have them run extended tests on your iMac, especially on the disk.  Your iMac is 5 years old, and it is possible your internal disk is starting to do more silent retries slowing down disk access.  I have a 2009 27" iMac and I'm on my 3rd internal disk replacement (granted, my model iMac was using a problematic disk drive model, but still rotating disk drives do wear out, so it would not hurt to have it tested).

Hey Bob,

I understand where you are headed with your theory 'bout the RAM, but I seriously doubt that mismatched RAM and RAM that has not been setup properly to make memory interleaving possible is really the cause of all of the excessive heat.

I have never heard of RAM modules causing the rest of a computer system to heat up to extremes and also still be quite warm at idle.

This iMac is still the last generation of what I like to affectionately call the thicker "iMac roaster pan" models.

I am betting that the OP's iMac has never been cleared of any noticeable dust, lint and dirt in its 5 year life cycle and it has accumulated a lot of internal crud impeding its ability to cool itself properly, any longer.

The OP's issues are not necessarily hardware or software related, but internal dirt build up related.

That is where my theory is  heading.

It might even be a problematic or failing internal power supply.

I definitely agree that the OP should take the iMac to the nearest Apple Store or nearest Apple authorised service center for a complete diagnosis and possible repair.

com.apple.dock.extra crash

I understand where you are headed with your theory 'bout the RAM, but I seriously doubt that mismatched RAM and RAM that has not been setup properly to make memory interleaving possible is really the cause of all of the excessive heat.

I have never heard of RAM modules causing the rest of a computer system to heat up to extremes and also still be quite warm at idle.

I do not think the RAM configuration is the problem.  The configuration is an oddity, and if nothing else mandi.w should at least arrange for the 2GB modules to be in the same DIMM0 slot.  But I do not think it would be causing all the problems reported, unless it was failing RAM, and then the configuration would still not matter.  Its odd configuration just drew my attention to it, and that made me think 3rd party RAM, and it can sometimes be the cause of system problems (although the typical result of failing RAM is a kernel panic, but while very rare, bad RAM does not always need to result in a panic to cause problems).