iMac temperature behaviour!

[athinamj]

My iMac is the 24'' with the 3.06 processor and I bought it on December 2008. A few months ago I installed Snow Leopard. Since then from time to time while my temperatures are normal without playing a game or something I notice that from 45C it reaches 70C all of a sudden. I monitor it through istat. If I reboot istat shows normal temperatures again!
Can someone tell me why does this happen or if someone has experienced something similar?

 

[simsaladimbamba]

Have a look at Activity Monitor (Applications / Utilities /) and select All Processes and sort by CPU to see what the culprit may be.

image below uses sorting by CPU as an example

 

[S.B.G]

Wow, even your low temp of 45C is way high for doing nothing. I have the exact same model iMac and mine usually runs at 36C-38C while idle.

Maybe your fans need cleaning or maybe one or more aren't working at all. What are your fans speeds showing in iStat?

 

[athinamj]

My fans work as follows:

CPU fan: 1198
HD Fan: 1275
Optical Drive: 698

I took my iMac 2 months ago to the service centre because I had to replace my screen so they cleaned it up for me.

I have only Firefox running now and my CPU Temp is 39C.

 

[TMRaven]

Might be a faulty sensor. Hardware check can tell you that. Other than that, do monitor processes all the time to see if anything correlates with your temperature spikes.

 

[athinamj]

They did a hardware check when I took it to service and everything was fine.
Next time it happens I will check Activity Monitor!