underclocking does little to the heat generated.
Most heat can be removed by reducing CPU/GPU and Core voltage (as well as ram).
In order for this to be successful, the core frequency needs to be lowered as a result.
It takes a bit of playing around, and testing.
You can try to do:
and add following lines in the file:
Test and see what the maximum and minimum frequency is you really need.
Lowering it too much, cripples the system, and makes it sluggish.
Sometimes just lowering the minimum frequency and leaving out the 'arm_freq' line, might give you what you need.
From my experience, it makes no sense to lower arm_freq_min below 200 (stock is 400 on a Pi 4), as the Pi will boost into high frequency as soon as you just move the mouse. So 250 is a relatively safe setting for small programs.
The settings also might not work on the Pi 4 (as this is a method that works on the Pi3 (B+)), but I think it should work on the pi4.
You can check the CPU frequency by typing:
It'll show you with what loads the CPU goes into boost speeds.
Sometimes setting the arm_freq_min value higher will prevent it from going into boost speeds, and keep the CPU cooler.
After you've confirmed what works well, you can adjust the voltage, by adding line underneath:
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Where you can decrease the negative values further, the lower you set the frequency.
Play around with the value. If your pi refuses to boot up, take the SD card into another computer, and load the 'config.txt' file in the root folder in a notepad editor, to reset the value to a bit higher.
You can also save heat by underclocking the RAM, core and GPU:
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Always start out by lowering the frequency on stock voltages first!
Then modify the over_voltage settings.
Test your system in idle, and doing small tasks when changing over_voltage_min settings,
And test under load, when lowering over_voltage settings.
Alternatively, you can always buy a larger cooler:
An active one: https://www.amazon.com/dp/B07TZFRVQJ
Or a passive one: https://www.amazon.com/dp/B07W5HXZFK/
The passive one is good enough to cool your Pi4 without a case (as the heat sink almost is the same size as a case), when using the Pi mostly with low demanding programs.
The active one, cools the pi best under load scenarios, or with programs that use more than 25% of CPU.