CPU Temperature suddenly raises from 75 °C to 100 °C

davidchunco,

On behalf of Tom's Moderator Team, welcome aboard!

If you ran the latest version of Prime95, then you can expect unrealistically high Core temperatures. Also, if you ran "Blend" rather than "Small FFT's" you can expect your Core temperatures to fluctuate. Here's why:

Intel tests their processors under carefully controlled conditions at 100% TDP. 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.

Do not use Prime95 versions later than 26.6 on 2nd through 8th Generation i3, i5 or i7 CPU's, which all 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 Core temperatures up to 20°C higher. The FPU test in the utility AIDA64 shows 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.

Please download, then run only Small FFT's for just 10 minutes.

• Prime95 v26.6 - http://www.mersenneforum.org/showthread.php?t=15504

If you’re overclocked and run AVX apps such as for rendering or transcoding, you may need to reduce Vcore and Core speed or upgrade your cooler and case fans so Core temperatures don’t reach 85°C. Many 6th, 7th and 8th Generation motherboards address the AVX problem by providing offset adjustments in BIOS, however your 4th Generation motherboard does not have this feature. Asus RealBench runs a realistic AVX workload typically within +/- a few % of TDP, and is an excellent utility for testing overall system stability, whether you're overclocked or not.

• Asus RealBench - http://rog.asus.com/rog-pro/realbench-v2-leaderboard/

Prime95's default test, Blend, is a fluctuating workload for testing memory stability, and Large FFT's combines CPU and memory tests. As such, Blend and Large FFT's both have fluctuating workloads which aren’t well suited for CPU thermal testing.

Other stability tests such as Linpack and Intel Burn Test have cycles that peak at 120% workload, which again aren’t well suited for CPU thermal testing. The test utility OCCT runs elements of Linpack and Prime95, which will terminate the CPU tests at 85°C.

The "Charts" in SpeedFan span 13 minutes, and show how each test creates different thermal signatures.

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.

Shown above from left to right: Small FFT's, Intel Extreme Tuning Utility CPU Test, and AIDA64 CPU Test.

Intel Extreme Tuning Utility is also a fluctuating workload. Although AIDA64's CPU test is a steady workload, it's far below TDP, which is insufficient for thermal testing. All other AIDA64 CPU test combinations are fluctuating workloads, which again aren't well suited for thermal testing. Also, AIDA64 is not Freeware, so the Trial version expires.

Here's the operating range for Core temperature:

Core temperatures above 85°C aren't recommended.

Core temperatures increase and decrease with Ambient temperature.

Highest Core temperatures occur during stress tests, rendering or transcoding, but are lower during less processor intensive workloads such as applications and gaming. CPU workloads and Core temperatures can vary greatly between games. Idle temperatures below 25°C are generally due to Ambient temperatures below 22°C.

If you'd like to get up to speed on this topic, learn how to properly test your Core temperatures and establish a valid thermal baseline, then please read this Sticky: Intel Temperature Guide - http://www.tomshardware.com/forum/id-1800828/intel-temperature-guide.html

Once again, welcome aboard!

CT