My Macbook 7.1 (Macbook white mid-2010) with 10gb ram and 250gb SSD Samsung 850 EVO overheats with very few apps open. It overheats for no particular reason. It cools down for no particular reason too. It goes from 89 to 65 in seconds regardless of applications usage that I do. Why is this happening?
Without seeing your Activity Monitor, it's tough to say what your CPU is doing. However, a 24 degree temp swing in a couple of seconds is a lot.
Have you tried AHT (Apple Hardware Test)?
My thinking is that you may have a bad temperature sensor (or it's getting bad info).
If that's the case, there are folks who repair things like this, or it just may be a good reason to upgrade your Mac. There is a guy in NY that does really good work (I am not affiliated) repairing these boards: https://mailin.repair/
I went on and opened the Macbook, detached the ventilator fan, cleaned it - there was a thick dust ball underneath it somewhere, returned everything back and voila! Rarely goes over 80C now.