My iMac graphics card is overheating
I have up graded my iMac early 2009 24" to El Capitan and now the graphics card is heating up so I have about 30 minutes before it reaches 100 degrees and have to sleep it . It is not dependant on what I do. It is also very slow. I have checked for viruses and cleaned the files but no difference.
iMac, OS X El Capitan (10.11.3)