Stresstesting OC'd CPU, frequency lowers to stock during test (i7-8700K)

[Vegard O]

Hi all, I don't know if this is the correct place to ask.

I'm trying to run a stresstest on my system, to see how the custom water cooling holds. Running an i7 8700k, OCd to 5 GHz. I use aida64 to stresstest, also tried prime64, same problem.

I use HWmonitor to watch temps, and I noticed whenever I start the stresstest (aida64 FPU), my CPU freq goes down to stock, 3.7 GHz, and it never rises above that (stresstested for hours). Does anyone know how to fix this? Tried to google, but found no solutions. Some saying it's temps, but it doesn't rise above 55C. Games like AC Origins, PUBG is running fine, temps are staying below 70.

Appreciate any tips I can get.

[Fiery]

It is most likely because under heavy stress your CPU is hitting the pre-configured TDP or power limits, and so it has to scale the clocks down to obey those limits.  You can either unlock those limits to avoid such issues, and/or disable Turbo Boost and use 5GHz as the base clock for your CPU.