i7 8700 High Package TDP and High Temps (when running fans at 100%)

Which version of Prime95?

Pezza349.

Do not run any versions of Prime95 later than 26.6. Here's why:

Intel tests their processors at a steady100% TDP workload. Prime95 version 26.6 Small FFT's is ideal for CPU thermal testing, because it's a steady 100% workload with steady Core temperatures that typically runs Core i variants with Hyperthreading and Core 2 processors within +/- a few % of TDP. No other utility so closely replicates Intel's proprietary test conditions. This is also the utility that Real Temp uses to test Core temperature sensors.

100% CPU Utilization in Windows Task Manager seldom equals 100% workload or TDP. When performing a thermal test, the objective is to run utilities that won't overload or underload you processor. Here’s a sample of utilities grouped as thermal and stability tests according to % of TDP, averaged across five Generations of processors at stock settings:

TDP ... Thermal Test - Steady Workload

129% ... Prime95 v27.7 through v29.4 - Small FFT’s (AVX, No Offset)
101% <-- Prime95 v26.6 - Small FFT’s
89% ... HeavyLoad v3.4.0.234 - Stress CPU
87% ... FurMark v1.19.1.0 - CPU Burner
78% ... CPU-Z v1.82.0 - Bench - Stress CPU
66% ... AIDA64 v5.95.4500 - System Stability Test - Stress CPU

TDP ... Stability Test - Fluctuating Workload (Peak)

123% ... OCCT v4.5.1 - CPU: OCCT (AVX, No Offset)
118% ... LinX v0.6.5 - Default
116% ... IntelBurn Test v2.54 - High
113% ... OCCT v4.5.1 - CPU: Linpack (AVX, No Offset)
110% ... AIDA64 v5.95.4500 - System Stability Test - Stress FPU
99% <-- Asus RealBench v2.56 - Stress Test (AVX, No Offset)
97% ... Intel Processor Diagnostic Tool v4.1.0.24 - Default
94% ... Sandra 2017.09.24.41 - Burn in - Processor Tests
92% ... CineBench v15.0 - CPU - Render Test
79% ... Intel Extreme Tuning Utility v6.4.1.15 - CPU Stress Test

All tests will show 100% CPU Utilization in Windows Task Manager, regardless of actual Workload. Higher TDP tests produce higher Core temperatures. Power (Watts) and Core temperatures will vary with Microarchitecture, Core count, Core speed, Core voltage, VID, Turbo Boost, Hyperthreading, Instruction Sets, Memory, IGPU, CPU cooler, BIOS versions and Microcode.

2nd through 8th Generation i3, i5 and i7 CPU's have AVX (Advanced Vector Extension) Instruction Sets. Prime95 versions later than 26.6 run AVX code on the CPU's Floating Point Unit (FPU) which causes unrealistic temperatures up to 20°C higher due to excessively high TDP workloads, as shown above. Other high TDP utilities have similar results.

AVX can be disabled in Prime95 versions later than 26.6 by inserting "CpuSupportsAVX=0" into the "local.txt" file in Prime95's folder. However, since Core temperatures will be the same as 26.6, it's easier to just use 26.6. AVX doesn't affect Core i 1st Generation, Core 2, Pentium or Celeron processors since they don't have AVX Instruction Sets.

• Download Prime95 version 26.6 - http://www.mersenneforum.org/showthread.php?t=15504

Run only Small FFT's for just 10 minutes.

Your Core temperatures will be up to 20°C lower. Give it a try.

This is what it looks like:

Shown above from left to right: Small FFT's, Blend, Linpack and Intel Burn Test.

Note the steady thermal signature of Small FFT's, which allows accurate measurements of Core temperatures. A steady 100% workload is crucial for thermal testing so the CPU, cooler, socket, motherboard and voltage regulators can thermally stabilize.

Also, if you'd like to get yourself up to speed on this topic, then read our Sticky: Intel Temperature Guide - http://www.tomshardware.com/forum/id-1800828/intel-temperature-guide.html

CT

Pezza349.

The Intel Temperature Guide actually says:

" ... Core temperatures above 85°C aren't recommended.

Core temperatures below 80°C are preferred.

Core temperatures increase and decrease with Ambient temperature. ... "

It also says:

" ... Although most processors Throttle at 100°C (212°F) ... it’s not advisable to run your CPU near it's thermal limit, just as common sense tells you not to run a vehicle with the temperature gauge pegged in the red "hot" zone.

If your hottest Core is near it’s specified Tj Max Throttle temperature, then your CPU is already too hot. The consensus among well informed and highly experienced system builders, overclockers and reviewers, is that cooler is better for ultimate stability, performance and longevity. Experts all agree that it's prudent to observe a reasonable thermal margin below Tj Max. So regardless of environmental conditions, hardware configurations, workloads or any other variables, Core temperatures above 85°C aren't recommended. ... "

Accordingly, you need to leave thermal headroom to accommodate the potential for running very heavy workloads, as well as an increase in seasonal ambient temperature.

Q What is your ambient (room) temperature?

If it's winter where you live, then your ambient temperature is most likely a few degrees below "standard" or normal, which is 22°C or 72°F. Since Core temperatures increase and decrease with ambient temperature, when the season changes to summer, your ambient temperature will likely be at least a few degrees above normal. This means your Core temperatures will increase just as much as your ambient temperature.

CT