I have a Thinkpad x230 that I thought was nearly dead, it kept on randomly shutting down every now and again. I considered overheating to be a possible cause of the issue, so I cleaned it as best as I could, but still, I got the random shutdowns. I slowly eliminated all other possibilities, such as software, dirty RAM and I had soon accepted the brutal fate that my laptop was near its demise. I began by searching on Ebay to find a likely replacement, but soon my lack of finances meant that I baulked at the price and was nevertheless outbid. Before I knew what I was doing I entered down the rabbit hole of cleaning my Thinkpad fan. It sounds simple, but there is a reason I've never done it before; I had to completely disassemble my laptop down to bare-bones of the motherboard and I even removed the wifi and Bluetooth card. I don't mind disassembly, but reassembly I find it a bit trickier. But hey I didn't have anything to lose, I was buying a new laptop anyway. After cleaning the fan and motherboard, I reapplied thermal paste and reassembled. The whole process took me hours. I was soon surprised to see my laptop rebooted and not only that, but my original problem was solved. So I expected this old workhorse has another two years in it yet.
I installed Psensors to check and saw that my laptop was now a lot cooler. I put it down mainly to the thermal paste that had completed worn out. I hadn't realised new paste would make such a difference. Next time I need to apply it a bit more thinly!