KEEP IT COOL
The Raspberry Pi 4 is unusual in its company, because it’s a warm little thing. We’ve seen users out there experiencing recorded temperatures of around 82 C sitting idle, which is (as you might imagine) not the finest thing to happen to your hardware.
Like most chips these days, the key components of the Pi 4 will thermal throttle when they get too hot: The CPU is set to throttle at 80 C, while the GPU joins it should the temperature make it to 85 C. If either of these things happens, you’ll see a thermometer pop up on your desktop, half full to represent the former situation, and full red when everything’s going into slow-down mode.
This mainly happens because these chips are being pushed. ARMv8 runs much harder and hotter than the cores of Raspberry Pis past. The first couple of editions could run happily with no cooling at all; the Pi 3 realistically necessitated a small heatsink on the major chips; run the Pi 4 raw, and you’re in a world of hurt.
So, a case is an absolute must. Irritatingly, the official red and white case from the Raspberry Pi foundation just compounds the problem, encasing the board in a toasty box that keeps it nice and insulated. You don’t absolutely have to go to the full extent of using a case with a microscopic built-in fan, or dropping on Pimoroni’s $10 Fan SHIM, though that will obviously keep it cool enough; the Aluminum Heatsink Case from The Pi Hut ($15) does a highly credible job of dissipating the heat from across, the board while still keeping things passive and silent.
If you want to see how hot your board is getting, run sudo vcgencmd measure_ temp in a command line to return your core temperature.