|Almost all CPUs these days have built-in thermal protection. Once they reach a certain trigger temperature, they begin to throttle back. If the temp gets too high, they shutdown completely.|
Is the 40C the system temp or CPU temp? Is it at idle or under load? If it's the CPU, it's within the normal range. If it's the system temp, it's a bit high but nothing to worry about, but it would probably mean the CPU temp is even higher than 40C & that *may* be a problem.
You need to be more specific about the temps & it would help to know the make/model of your CPU. Why would you want your system on all the time?