glazor,
On behalf of Tom's Moderator Team, welcome aboard!
IETU is a fluctuating workload, which is precisely why you're seeing fluctuating Core temperatures. If you instead run a steady-state workload, you'll see steady Core temperatures.
The "Charts" in SpeedFan span 13 minutes, and show how each test creates distinct thermal signatures.
Shown above from left to right: Prime95 Small FFT's, Blend, Linpack and IntelBurn Test.
Note the
steady thermal signature of Small FFT's, which allows accurate measurements of Core temperatures.
A steady 100% workload is key for thermal testing so the CPU, cooler, socket, motherboard and voltage regulators can thermally stabilize.
Shown above from left to right: Prime95 Small FFT's, Intel Extreme Tuning Utility CPU Test, and AIDA64 CPU Test.
“Stress” tests vary widely and can be characterized into two categories;
stability tests which are
fluctuating workloads, and
thermal tests which are
steady workloads. Prime95 v29.8 Small FFT's
(AVX disabled) is ideally suited for testing thermal performance, because it conforms to Intel's Datasheets as a
steady 100% workload with
steady Core temperatures. No other utility can so closely replicate Intel's thermal test workload.
Utilities that don't
overload or
underload your processor will give you a valid thermal baseline. Here’s a comparison of utilities grouped as
thermal and
stability tests according to % of TDP, averaged across six processor Generations at stock settings rounded to the nearest 5%:
Although these tests range from
70% to 130% TDP workload, Windows Task Manager interprets every test as
100% CPU Utilization, which is processor resource activity,
not actual workload.
Core temperatures respond directly to Power consumption (Watts), which is driven by workload. Prime95 v29.8 Small FFT’s
(AVX disabled) provides a
steady 100% workload, even when TDP is exceeded by overclocking. If Core temperatures don't exceed
85°C, your CPU should run the most demanding
real-world workloads without overheating.
We actually have a Guide for this topic:
Intel Temperature Guide -
https://forums.tomshardware.com/threads/intel-temperature-guide.1488337/
It's a "Sticky" near the top of the CPUs Forum; if you look there you can't miss it. I suggest you read the entire Guide, but pay especially close attention to
Section 11 - Thermal Test Basics.
Once again, welcome aboard!
CT