Well I have to admit (not for the first time) that I can be blissfully ignorant sometimes. My previous post, Can a Raspberry Pi 4 really replace your PC, was intended to look at the obvious issue described in the title; instead, I walked face-first into a huge controversy about the "normal" operating temperature of the Raspberry Pi 4, and the design of the Official Raspberry Pi 4 case. There are currently 22 pages on this topic in the Raspberry Pi Forums, and the discussion is ongoing.
To summarize, there are two separate but related problems (both of which I noticed and commented on in the original post): the Raspberry Pi 4 runs relatively hot, and the Official Raspberry Pi 4 Case has poor ventilation.
When you combine these two problems, the result is that the "idle" temperature is something like 70 Centigrade, and it takes relatively little load to push the temperature over 80 Centigrade, into the range where CPU throttling is automatically applied.
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That's not good for several reasons - first, it makes the performance of the Pi 4 look very bad (well, duh, it's running at 600MHz instead of 1500 MHz), and it actually heats up the metal shields around the USB and RJ-45 connectors so much that they become very uncomfortable to the touch.
The situation with the temperature honestly doesn't surprise me. This is something that has been going on throughout the development of the Raspberry Pi family. Just about every new model has been more powerful than the previous models, and has generated more heat than the previous models.
Considering the size of the step forward that the Pi 4 takes from previous models, why would the situation be any different now?
The thing that does surprise me, though, is the design of the new case. I mean, honestly, the Raspberry Pi 3 case was an absolutely brilliant design for exactly this reason. Just look at the picture on the right... both side panels and the entire top can be removed to allow for airflow!
Contrast that with the Pi 4 case, where your only option to get air is to remove the entire top of the case, which leaves the Pi 4 completely exposed.
The impact of this problem is particularly severe in exactly the situation that I wrote about originally - someone wanting to use a Pi 4 as a desktop system. The Raspberry Pi Foundation offers a "Desktop Kit", which includes an Official Pi 4 Case... Sigh.
I have defended the Raspberry Pi developers in several previous cases of design flaws or just plain mistakes, because they were in areas which were at least less obvious and dealt with some rather obscure technical areas or unusual configurations, but this one just seems blindingly obvious.
OK, well, be that as it may, the question now is what to do about it. The immediate answer to that question is if you have a Pi 4 running, take the top of the case off. You and your Raspberry Pi will be a lot happier that way.
Beyond that, if you are using your Pi 4 in a situation where you don't really need the case on it, remove it completely, and if possible set up the Pi 4 to run in a vertical position, to improve air flow across the board and heat removal from both sides of the board.
As I said at the end of the previous post, I have ordered another different case which has a bit better ventilation than either of the two I have right now. I have also ordered a couple of different heat sinks, and a "shim fan".
I hope that will all arrive in time for me to try it out over the weekend, so I can pass along some more information about temperatures, and about what pieces fit together in which cases, if any.
Finally, the Raspberry Pi Foundation says that they are working on several software and firmware changes that should help bring the temperature of the Pi 4 down.
Hopefully those will be released soon - but even if they are, I don't expect that they will improve the situation by more than 5 degrees or so, and given how hot the Pi 4 runs, that is not enough to eliminate the need for the kind of hardware measures I am looking at now.