My ThinkPad E480 has been running a little loud lately and from what I hear (see what I did there? 😉 ), Lenovo can put poor thermal paste on their laptops. I often run a lot of things at a given time like an IDE, sometimes a VM and the usual three, Firefox, Evolution Mail and Spotify. I thought the fan being loud was due to my workload and probably due to GNOME being a resource hog but after replacing the thermal paste, I was pleasantly surprised to find that the computer not only ran quieter but also cooler at high loads.
The thermal paste I used is called Arctic MX-4 and I simply applied two small blobs on the exposed heat spreaders. Of course you want to fully clean both the heatsink and CPU die with a tissue before you apply the new thermal paste. The entire process took about five minutes as removing the heatsink was super easy. When you do remove the heatsink assembly, be careful when disconnecting the CPU fan as the wire is fragile and should not be tugged.
By stressing the machine a little for about 10 minutes, the temperatures would stabilise at 65-68C with ambient being 25C. There are moments when the temperature would spike up to 70-80C but when the fans kick in, the temperature drops into the mid sixties. What I did was run fishgl.com, a Windows 10 VM and Minecraft all at once and those were the results.
As for idle, you can expect as low as 35C with an average idle of 45-50C. Of course, it depends on the ambient temperature as well.