Is Prime95 Max Temp 90 C Normal for a i7-4790K 4.0GHz

Even 80C in gaming with the CPU at stock sounds pretty hot, but it's not unreasonable. I wouldn't ever use the new versions of prime95, they cause the voltage to creep up as you continue to run the test last I heard and cause unreasonable temps. Are you sure that you clamped the cooler down properly and that there's enough thermal paste? Is there an option to raise the pump speed in the corsair link software?

Prime95 isn't the best for actually seeing how hot your CPU will get, because it doesn't really represent the real world.
The 4790k does run pretty hot though, but your fluctuations may be because your CPU cooler isn't at 100% until the temps get higher.

samzhaizhai,

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

At the top of all our Forums are "Stickies" which are informative Threads permanently "stuck" in place so they're always available as references for everyone's benefit. Near the top of the CPU's Forum you'll see a Sticky you might want to read: Intel Temperature Guide - http://www.tomshardware.com/forum/id-1800828/intel-temperature-guide.html

Here's the typical operating range for Core temperature:

85°C Hot (100% Workload)
75°C Warm
65°C Norm
55°C Norm
45°C Norm
35°C Cool
25°C Cold (Idle)

Q: Which version of Prime95 did you run?

Do not use Prime95 versions later than 26.6 on 2nd through 7th Generation i3, i5 or i7 CPU's, which all have AVX (Advanced Vector Extension) Instruction Sets. Recent versions of Prime95 such as 28.9 run AVX code on the CPU's Floating Point Unit (FPU) which causes unrealistic temperatures up to 20°C higher. The FPU test in the utility AIDA64 shows similar results.

From Intel: Troubleshooting Intel® Core™ i7-4790K / i5-4690K overheating - https://communities.intel.com/docs/DOC-23517 - "Overheating occurs very quickly on motherboard products with certain BIOS settings when running the Small FFT test that is part of the Prime95 application, version 28.5." - "Overheating is not as severe with earlier versions of Prime95 ... "

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: http://www.mersenneforum.org/showthread.php?t=15504

Contrary to James Mason's comment, 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 Thermal Design Power (TDP) at stock settings. As Intel tests their processors under carefully controlled conditions at 100% TDP, no other utility so closely replicates Intel's test conditions. This is also the utility that Real Temp uses to test Core temperature sensors.

Although Prime95 v26.6 Small FFT's is ideal for thermal testing, Asus RealBench is ideal for stability testing: - http://rog.asus.com/rog-pro/realbench-v2-leaderboard/

Concerning Core temperature fluctuations or "spikes", Core temperatures respond instantly to changes in load. Intel’s specification for Digital Thermal Sensor (DTS) response time is 256 milliseconds, or about 1/4th of a second. Since Windows has dozens of Processes and Services running in the background, it’s normal to see rapid and random Core temperature “spikes” or fluctuations during the first few minutes after startup, which should eventually settle. Any software activity will show some percentage of CPU Utilization in Task Manager, where unnecessary Tray items, Startups, Processes and Services that contribute to excessive or continued spiking can be disabled.

Once again, welcome aboard!

CT

samzhaizhai,

As you may know, 2nd Generation and earlier processors use Indium solder between the Die and the Integrated Heat Spreader (IHS), while 3rd through 7th Generation use Thermal Interface Material (TIM), which has much lower thermal conductivity than solder. Consequently, 3rd and 4th Generation 22 nanometer processors, and especially 5th through 7th Generation 14 nanometer processors suffer from temperature and spiking problems, which is detailed in the Guide I linked for you.

Spiking is inherent to these processors. Other than cleaning up your tray startups, processes and services, reducing Core voltage, improving cooling or de-lidding you CPU, there's little else you can do to minimize spiking. As long as your rig is stable and Core temperatures don't exceed low 80's, I wouldn't lose any sleep over it. Enjoy your new rig!

CT