Question Intel i5 6400 abnormally low cpu temp and tdp

Mar 22, 2019
I was running aida 64 on my friends machine when I noticed his cpu temps were in the 40s and his tdp didn't exceed 35W his cpu usage was at 100% and after overclocking with a special bios to 4.3 the temps only got to 46 and the tdp was 42W when it's rated for 65. I was originally doing this stress test because he was complaining about his games running slow and after comparing with other people's results it scored a higher result on the user benchmark 91% better. Just wandering what I can do to help him he has a asus z170-p 3d bios Vers. 8002 cpu cooler hyper 212. I checked the psu voltages and everything was within the margin


... aida 64 ... tdp didn't exceed 35W ... usage was at 100% ... overclocking ... to 4.3 the ... tdp was 42W when it's rated for 65 ... cpu cooler hyper 212 ...

On behalf of Tom's Moderator Team, welcome aboard! Thank you for asking a very interesting question.

TDP values, actual power consumption (Watts) and Core temperatures are all directly related to workload, so you need to be using the proper utility and test to get a 100% TDP workload. As such, there are several variables which need to be taken into account.

Although much of the following emphasizes thermal testing, it also applies equally to TDP.

“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 version 26.6 Small FFT's is ideal for CPU thermal testing, because it's a steady 100% workload with steady Core temperatures. No other utility so closely replicates Intel's load test.

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%:

All tests will show 100% CPU Utilization in Windows Task Manager, which indicates processor resource activity, not % TDP workload. In other words, while CPU Utilization max's out at 100%, TDP workload can reach up to 130%, as shown in the scale above. So instead of monitoring CPU Utilization, the most simple and revealing indication of % TDP workload is to monitor CPU Package Power consumption (Watts) with the monitoring utility "Core Temp".

Core temperatures respond directly to Power consumption (Watts), which is driven by workload. AIDA64 has 15 possible CPU related stress test selections which yield 15 different Power values (Watts) and Core temperatures. The individual CPU test is just 70% TDP. Only the CPU/FPU test combination is about 100% TDP workload. Prime95 v26.6 Small FFT’s provides a true and steady 100% TDP workload.

Measured TDP may vary from rated TDP among the same CPU models. Also, motherboard stock settings may vary from Intel stock settings. TDP specifications are derived from the fastest Hyperthreaded variants for X-Series, Extreme, i9's, i7's and i3's. Since i5’s follow i7 designs with 25% less cache and disabled Hyperthreading, Pentiums and Celerons similarly follow i3 designs. As such, slower variants without Hyperthreading typically don't reach TDP.

For example, the i7 6700K and i5 6600K are both rated at 91 Watts TDP, yet the slower i5 without Hyperthreading doesn't reach TDP, which favorably affects Core temperatures. If the fastest Hyperthreaded variants for X-Series, Extreme, i9’s, i7’s and i3’s run Prime95 v26.6 Small FFT’s using Intel’s stock BIOS settings, the processors will show steady Core temperatures and Power consumption (Watts) within +/- a few % of TDP.

This verifies that Prime95 v26.6 Small FFT’s is a valid 100% workload. It scales appropriately on all processors, whether at stock settings or overclocked. I strongly recommend that you use Prime95 v26.6 Small FFT's. Do NOT use any later versions such as 27.7 through 29.4 due to AVX Instruction Sets.

• Prime95 v26.6 (non-AVX) -

Run only Small FFT's.

Regardless, it's unlikely that your overclocked i5 will ever approach 65 Watts. As similarly explained above, TDP for the 6th Generation i5 6600, 6500 and 6400 are derived from the Hyperthreaded 65 Watt TDP i7 6700. Consequently, none of these i5's can reach TDP. Only the i5 6600K may reach or exceed your TDP.

You might want to read Section 11 - Thermal Test Basics: Intel Temperature Guide -

Once again, welcome aboard!

CT 😎
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