Overheating

Last year my X200 started to overheat when I stressed its CPU's. After various research I decided it was a hardware problem - even setting the fan in disengaged all the time did not help. It quickly went over 90°C and then shut off brutally from hardware protection circuitry. After such shutoff, you can't start the laptop (it's not even taking charge) until you have briefly removed power and battery.

Without much confidence it would help, I disassembled the thing enough to check the silicon grease between the CPU and the cooler. There was little grease at the CPU, and no grease at the other chip (graphics? I don't know). I put a generous dab of grease in both places and reassembled.

This completely solved the problem. I can now ran at 100% CPU on both cores continuosly, and the temps hardly go over 60°C. What I can't understand is why I waited half a year before I tried this.

I'm a semi professional but this was quite an easy job. All that is needed is a Phillips #1 screwdriver and the Hardware Maintenance manual. And some silicon grease of course.