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My MPB has had this problem for years every time the ambient temperature gets a bit warmer. It starts in the spring and gets ridiculous during the summer.

The MBP clocks down its processor to 0.8 GHz, making it pretty much unusable. This happens as soon as some process-demanding apps (like NodeJS or Unity) are running on the machine.

However, the CPU temperature is just fine, between 60 and 80 degrees Celsius. It doesn't look like a thermal problem. Thus, I don't understand why this happens?

I tried every hint I found on the internet, including resetting SMC and NRAM, I even re-installed macOS.

Because this has happened from day one, I have been at the Apple Store many times, and the MBP now has its 4th logic board (!) Still, the problem remains.

What else might cause this strange phenomenon? I'm at a loss!

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    It's not just the CPU temp that can cause a throttle down, there are other temp sensor that feed input to the SMC. Use a tool like iStat Menu to get all the temp readings. Another question would be where are you using this MBP that seasonal changes create the issue? Also, what are the fans doing? – Allan Apr 19 '18 at 17:59
  • "Where" is not so much interesting as at which ambient temperature (AC or not?); also: how many peripherals are attached, does this happen on battery or plugged in? In any case, follow Allan's request and post more sensor readings as well. Since I do not use Unity or NodeJS much: any other "demanding apps" running? Last system install time, caches cleared? – LangLangC Apr 19 '18 at 19:56
  • Regarding the where and the temperature: It even happens in German spring time, which means about 25°C, which is not that much. The fans are running at full speed as soon as I start the Mac (takes about 20secs until they reach their max). But I now have a suspicion: It gets much worse if a monitor or dock is attached via Thunderbolt. If I detach it, the CPU speed goes back to normal after a while, but the fans are still running loud. – waldgeist Apr 20 '18 at 18:24

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