Safe temp for intel core i5 4670k?

Nice overclock at such a low Vcore. What is your Ambient temperature? Which Prime95 test are you running? Which temperature monitoring utility are you using? What type cooler are you using?

Intel's Thermal Specification - http://ark.intel.com/products/75048/Intel-Core-i5-4670K-Processor-6M-Cache-up-to-3_80-GHz - for your i5 4670K is 72C, however, the technical definition of their specification is very complicated, so I'll break it down for you.

There are 5 thermal sensors in a 4 core processor; a single Analog sensor (CPU temperature) and 4 individual Digital sensors (Core temperatures).

The temperature shown in Intel's specification, (Tcase), is measured on the surface of the Integrated Heat Spreader (IHS) under tightly controlled laboratory conditions at 22C Standard Ambient (intake temperature). For lab testing only, a groove is cut into the surface of the IHS where a thermocouple is embedded at the center. The stock cooler is attached, and a steady-state 100% workload is applied, (such as Prime95 Small FFT's). Thermal saturation is reached within 10 minutes.

Since there is no thermocouple on any processors outside Intel's labs in the wholesale or retail outlets, a single Analog Thermal Diode is instead used to "emulate" a thermocouple. This single analog sensor is located in the center of the lower layers of the processor package and is called "CPU" temperature, which is the equivalent of "Tcase".

The analog value is converted to digital (A to D) by the Super I/O (Input / Output) chip on the motherboard, then is calibrated to look-up tables coded into BIOS, which are all too often inaccurate. This is the temperature you see in BIOS and in monitoring utilities such as AI suite II, which are provided by motherboard manufacturers.

"Core" temperature, also called "Tjunction", is measured at the heat source by an individual Digital Thermal Sensor (DTS) for each Core, which are factory calibrated. Since the CPU sensor is not in relatively close proximity to the heat source, there is ~5C thermal gradient or "offset" between "Core" temperature and "CPU" temperature during Prime95 Small FFT's.

This means that Intel's "CPU" temperature (Tcase specification) runs ~5C less than "Core" temperatures. More correctly, since there is always some temperature sensor discrepancies between Cores, "average" Core temperature is most important. So if Prime95 Small FFT's is run for 10 minutes at 22C Ambient, then the average Core temperature is ~77C.

Standard Ambient = 22C
Tcase (CPU Temp) = 72C
CPU / Core Offset + 5C
Tjunction (Core Temp) = 77C
Tj Max (Shutdown Temp) = 105C

Tj Max is Intel's Thermal Specification which defines the "Core" temperature at which the processor will shutdown. Excessive heat kills electronics. Most folks in the overclocking community will agree that any sustained temperatures greater than 75'ish are just too hot for a 12 hour stability test or for processor longevity.

Bottom line? Your Core temperatures are within Intel's specs. You're OK up to 75'ish, but remember that when running Prime95 Small FFT's, if you're testing below or above 22C Standard Ambient, then you need to add or subtract the difference so that your test results are corrected to Intel's standards. This way you eliminate variables, and your results will always be consistent and repeatable.

Some additional thoughts to keep in mind - Thermal Testing:

Prime95 Small FFT's is the standard for processor thermal testing, because it's a steady-state 100% workload. This is the test that Real Temp uses to test sensor movement. Prime95's default test, Blend, is a cyclic workload for testing memory stability, and is not suitable for thermal testing. Other tests such as IBT (Intel Burn Test) have segments which flood all registers with all one's, which is the equivalent of a 110% workload. While suitable for stability testing, IBT is uncharacteristic of real-world maximum loads. You can see for yourself by using the "Graphs" in SpeedFan to illustrate and compare how these tests create different thermal behaviors. On air cooling, thermal saturation is typically reached within 10 minutes, however on liquid cooling, saturation may require up to 30 minutes.

I hope this answers any questions you may have about processor temperatures.

Comp