Hi,

I'm running BOINC on a 21,5' iMac, 2,7 GHz Intel Core i5 Processor, 16 Go RAM.
CPU Core temperatures are PERMANENTLY around 85°C, even with calculation settings down to 20%

After quitting BOINC, the temperatures fall down to 62°C within 1 minute, 50°C within 2 minutes. Average temperatures by "normal" use (i.e. BOINC is down) are around 35°C. They climb back to 70°C within 6 minutes after BOINC relaunch.

Macs Fan Control drops those temperatures down to 75°C, wich is still quite high, isn'it?

What's cooking ? Is it safe to keep the app running with such temperatures? What are the right settings (if any) to avoid such high temperatures?

Thanks for help.

What are the right settings (if any) to avoid such high temperatures?

The only way to overcome high temperatures is better -after market- cooling. And then preferably water cooling. Not all PC/Mac cases are capable of fitting after market fans or water cooling.

Is it normal for Seti to run those temperatures? Well, yes it is. You're doing intense calculations on your computer, on the CPU, so that will heat up. When the computer isn't running BOINC, it's idle, it's not using the CPU that much.

So when in high use you'll see heat up.
A good idea is to add filters to the PC case, on all openings, to keep hair and dust out. It's also a good idea to clean out the inside of the computer at least once a year, if you're in a dusty environment, make that two or more.

My i5-2500K reached low 80 centigrade with the 'normal' after market CPU cooler, I then changed to a Cooler Master Hyper Evo which took temps down to around 65 centigrade. Since about last summer, I changed over to a Cooler Master Seidon V2 water cooling setup, and now temps don't come above 55 centigrade. I also changed to a new case, with four 120mm fans and filters all around. They're doing a good job of keeping the cat hair out. :)

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Since the iMac tend to be a solid shell machine, he's going to have a hard time cooling that machine down.

I'd probably suggest cutting down the number of core he's using in his preferences so that it read

Use at most 50%.

Most macs have that issue as they don't really consider cooling when they build their computers