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I have a RPi4 now, have cooling sinks mounted on the processors and it runs pretty smooth, but sometimes I worry about the temperature development of my processor. At what level should I worry, and consider a fan?

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    I have a Pi4 with a camera setting in a window that gets direct sunlight, where the temperature would get above 60 Degrees C without any fan, and with the fan it maintains at 60 or below.
    – jwbradley
    Aug 23 at 14:22
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    Does this answer your question? Do i need a fan, or will ventilation holes suffice?
    – Seamus
    Aug 23 at 17:11
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    Is it just processor temperature that concerns you? My RPi got very hot in its first case, and stopped working. It turned out the RPi itself was fine, but the SD card was toast.
    – Simon
    Aug 24 at 13:33
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You needn't worry at all if your only concern is temperature. All RPi models have a built-in closed-loop thermal control system that will prevent your RPi from overheating. This system operates by reducing the operating frequency and core voltage when the temperature reaches set limits. These frequency & voltage reductions are called throttling. Throttling reduces the power consumed in the SoC, which reduces heat/temperature - it also reduces performance of the system.

Understanding the operation of the RPi thermal management system might lead one to reconsider the question you have posed. You can see now that since the system manages temperature, performance is the variable one must reckon with. And so I say the answer to your question is this:

Consider a fan only when your RPi is being throttled to the point that its performance becomes insufficient to meet your needs.

Wrt the relationships between temperature and performance, there are numerous other details you may wish to explore. While the RPi's thermal management system is implemented in proprietary firmware, there are user-accessible configuration parameters available in the RPi that allow you to change some aspects of its performance. If you're interested in details, you might begin here.

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    For the record: "When the core temperature is between 80°C and 85°C, a warning icon showing a red half-filled thermometer will be displayed, and the ARM cores will be progressively throttled back. If the temperature reaches 85°C, an icon showing a fully filled thermometer will be displayed, and both the ARM cores and the GPU will be throttled back."
    – Mast
    Aug 24 at 15:52
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Simple answer Never.

You should consider reading the official Documentation, rather than asking others to search for you. (Current Documentation leaves much to be desired, but if you read it all the answers are there.)

See https://www.raspberrypi.org/documentation/computers/config_txt.html#monitoring-core-temperature

When I got my Pi4 (just after the release) it got hot and I installed fans. With the firmware improvements if NEVER turns on. Even a stress test takes some time to raise the temperature to 60℃.

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    If you don't want to answer, simply don't. Otherwise your boldness is way out of line. I reject thereby your assumptions: I didn't ask to search for me. I asked for experiences and best practices of others so that I can learn from that. I was always learned to be polite and that there is no such thing as stupid questions; only stupid answers. But thanks anyhow for sharing your experiences.
    – Wolk9
    Aug 23 at 12:56
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    @Wolk9 The link provided is very clear, you should use a fan above 80 degrees C. At 85 degrees C you will a see serious reduction in performance.
    – pacmaninbw
    Aug 23 at 16:29
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    @Wolk9 I am sorry you feel this way. I have been teaching programming and statistics (among other things) for more than 40 years. I have always encouraged people to research their own answers, rather than just relying on others; that way you LEARN and are more likely to remember. Indeed I do not "know" the answers to most questions, even things I have done before BUT I know HOW to find the answers. Incidentally ½ of the answers on this site are wrong (or at least not the most efficient or best practice).
    – Milliways
    Aug 24 at 7:11
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    @Milliways. Thanks for your reply. I appreciate your honesty. I do agree that research is the best way to learn so I understand your goal. I was annoyed by the boldness of the way of saying. The good part of StackExchange is that the good and helpfull answers organically wil rise and bad ones will fall. I'm greatfull for all shares of experiences of others as they are often not written in manuals. They are the very reason for existence of fora like this.
    – Wolk9
    Aug 24 at 9:42
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As long as power concerns aren't an issue, consider adding a fan at any point. You can even get "silent" fans, so noise shouldn't even be an issue, except for in very quiet areas.

Even if the Pi doesn't strictly need it, it won't hurt, either. In the 30+ years I've had computers (and repaired them professionally for 15 years), I've never had a problem running one with too big a heat sink, too much airflow, or too many fans. In fact, I haven't had a hard drive fail since adding active cooling to them.

If your Pi is going through a lot of heat cycles, you could risk the solder becoming brittle or something warping to cease working. There's more reasons to having a fan than it simply overheating.

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