Could you have a look at the 2 main system logs to see what your MacOS may be busy at.
terminal or an
xterm window, the 2 following commands fired when the
problem appears may help you diagnose it:
tail -f /var/log/kernel.log
tail -f /var/log/system.log
To help anyone help you, next time this kind of problem arises, could you run the following command (within a
top -o cpu
and grab a copy of the topmost 10 lines to put them back within your original question as here:
Processes: 50 total, 3 running, 47 sleeping, 243 threads 12:18:07
Load Avg: 1.40, 1.53, 1.28 CPU usage: 5.97% user, 7.14% sys, 86.88% idle SharedLibs: 5044K resident, 9292K data, 0B linkedit. MemRegions: 10733 total, 769M resident, 15M private, 1479M shared.
PhysMem: 755M wired, 1363M active, 641M inactive, 2760M used, 1207M free. VM: 120G vsize, 1041M framework vsize, 2798981(19) pageins, 173(0) pageouts.
Networks: packets: 61207/73M in, 66123/6062K out. Disks: 877183/26G read, 171220/22G written.
PID COMMAND %CPU TIME #TH #WQ #POR #MREG RPRVT RSHRD RSIZE VPRVT VSIZE PGRP PPID STATE UID FAULTS COW MSGSENT MSGRECV SYSBSD SYSMACH CSW PAGEINS
1530 mdworker 17.1 06:56.12 4/1 2 82+ 384+ 39M+ 16M 143M+ 196M+ 2586M+ 1530 1 running 501 1946213+ 727+ 881948+ 219072+ 6484219+ 676187+ 679401+ 1914+
0- kernel_task 14.0 07:55.29 69/4 0 2 757- 22M 0B 130M- 75M 2355M- 0 0 running 0 26279 0 33251333+ 32358872+ 0 0 10243109 0
1522 mds 12.6 14:55.33 9 8 118- 862 361M+ 6052K 239M+ 1334M+ 3736M+ 1522 1 sleeping 0 13373455+ 1286 12149111+ 6697348+ 16039295+ 6938357+ 3331251+ 1819924+
This is an example of a problem (no I don't have the same problem ☺) where my Mac was overheating like a fool.
Here the 2 processes involved are
mdworker and are caused by
Spotlight indexing an external drive of 500 Go of backups
which I just plugged on.
The 2 involved tasks regularly topped to 200% cpu alltogether.
Spotlight is very inconspicuous about this behind the scene heavy business. It does just display a small point at the center of its looking glass within the menu bar.
When I finally clearly saw what was happening under the hood, I decided to let
spotlight finish its job, and one hour later, the temperature, the processors and the fans returned to a normal life.
Finally, since your OS (Mountain Lion) is Lion or more recent, I advise you to read this great explanation on
and if you feel comfortable reading system logs, try it.