Currently Being ModeratedMay 9, 2013 1:18 PM (in response to Addes)
There is something wrong as the computer should not heat up like that, but it has nothing to do with the thermal paste (unless there isn't any.) Is the fan actually running? Does it run at maximum speed when the computer is very hot or is it running at idle speed? If the latter then there could be a failed sensor. Have you tried resetting the SMC: Intel-based Macs: Resetting the System Management Controller (SMC)? Also check that there is nothing blocking the air vents.
In any event it would be wise to take the computer in for service. Continually using it at high temps will only cause damage.
Currently Being ModeratedMay 9, 2013 1:29 PM (in response to Kappy)
Apologies, I forgot to mention that I did the PRAM and SMC resets.
Airvents are unobstructed and the fan is at 6250 rpm, I've set it to max with SMC fan control.
I agree about the service part but I'm in a foreign country (east europe), ~500 miles from an apple center and the local shops are a bit.. shady. I think fixing it myself would be the best option, if we can identify the problem.
How do you know it's not the paste? Perhaps that's just not an issue on macs, I don't know really.
Currently Being ModeratedMay 9, 2013 1:37 PM (in response to Addes)
Well, without a proper diagnostic device I'm not sure how to identify the problem. If it's related to a bad sensor then that means replacing the sensor or the motherboard depending on whether the sensor is an independent part. If the SMC is defective then that means replacing the motherboard. So, I don't know how you would fix it yourself since you must get the parts. Given the potential cost to repair it (if it's repairable) you may spend more than the computer is worth given its age.
If you have the original discs that came with the computer you can run the software Apple Hardware Test to see if it identifies anything that is failing:
Running Apple Hardware Test on Intel Macs
Boot from the OS X Installer Disc One that came with the computer. After the chime press and hold down the "D" key until the diagnostic screen appears. Run the extended tests repeatedly for at least one or two hours. Note down any error messages if they appear. You will need to report them to the Apple tech who will service your machine.