Instructions
Look for spontaneous shutdowns. A PS3 that overheats may beep and turn itself off when it becomes too hot.
Look for video lag and stuttering. Overheated PS3 systems slow down and may not be able to render some games effectively.
Watch the screen for visual errors, such as artifacting. This occurs when the PS3 is unable to properly swap its memory buffers or the video card begins to malfunction from heat.