The CPU on my 2 month old MESH machine has been running at just around the max temp of 71 C recently, on just 50% load. It wasnt running this hot when I first got it. Dust is the obvious cause but I can see into my machine without taking the side panel off and it looked pretty clean, a little collecting on the 120mm exhaust fan, though not much, a little on top of the graphics card and that seemed to be it.
But given that it is so close to the max I thought I had better get in there and have a look and I find that about 80% of the total amount of the dust inside of the case has been trapped by the CPU heatsink. The separation of the fins is very small and the area beneath the fan was completely clogged. I know this sort of thing happens, but in two months, when everything else is fine?? Going in every couple of months to clean it out is hardly a chore, but when I point the vacuum cleaner at it, nothing moves and I have to remove the heatsink from the CPU and then unscrew the fan from the top of that in order to clear the fins. Now that is something I wont be doing every couple of months, mainly due to the risk of doing something some damage or not getting a good enough thermal contact when I replace the heatsink, so will need to look for a different cooling system for the CPU.
Another surprising thing that I found when I went in there was that there only appear to be two fan headers on the ASUS mainboard, and both of them are in use. I was thinking that I might add another 120mm fan if I couldnt find what the temperature problem was, but there was no header to connect it to.
The CPU temp is now down to 46/47 C at 50% load and I have closed off the grille just above the CPU/heatsink and will give it a while to see if this keeps some of the dust at bay.