10
Jan
2016

AMD CPU’s reporting lower than ambient idle temperatures? Here’s why!

It has to be said that the universe is pretty strict when it comes to fundamental law breaking. The First Law of Thermodynamics states that energy cannot be created or destroyed, and this goes the same with heatsinks. It is physically impossible to cool anything down to below the temperature of the air you are trying to cool it with, no matter how many Delta 4000 RPM fans you are using.

So why then, AMD, do your temperature sensors for everything after the FX series launched, report something like 10°C when idle when it’s about 20°C in the room?

IdleTemps

Under load, they seem to be a bit on the low side too:

LoadTemps

I am running an AMD FX-6300 clocked at 4.2GHz using a CoolerMaster Hyper 212 Plus (the precursor to the Evo). But have you noticed something? There are two temperature sensors being reported by AIDA64: one for the CPU cores (there seems to be only one sensor – each core is showing the same value even though there are six of them) and one for the CPU socket temperature.

It seems that the CPU socket temperature is more realistic than the CPU core temperatures, and the BIOS on the AsRock 970m Pro3 seems to adjust fan speeds in accordance with the CPU socket temperatures rather than the core temperatures. So what is going on then?

Time to do some digging. It seems that AMD’s temperature sensors use a different algorithm than normal sensors. This is probably done to report more accurate load temperatures than idle temperatures – since the difference between CPU Cores and CPU Socket at load is much less than the difference reported at idle (Load= 21°C, Idle = 8°C). How can we be sure of this? Time to use AMD OverDrive (AMD’s own system monitoring and overclocking utility – so should have this algorithm accounted for).

OverDriveIdle

Interesting. They report temperatures as Thermal Margins in OverDrive (AIDA was reporting a core temperature of 10°C when I took the screenshot). Time to load it up and see what we get:

OverDriveload

Under load, the Thermal Margin decreases. AIDA reported a core temperature of 41°C when the screenshot above was taken. So it seems then, that the maximum safe temperature for CPU Core temperature is 70°C with my CPU. But this also means that AMD OverDrive does not offset the reported temperatures at all. It also reports inaccurate temperatures at idle.

This isn’t a huge problem, since you are almost never concerned about idle temperatures. If you are overclocking on the AMD FX platform (or other platforms where AMD uses this weird temperature setup), then just make sure you don’t go over 70°C on the CPU Core temperature. Other than that, you should be golden. BIOSes seem to use the CPU Socket temperature for adjusting fan speeds – I set mine to 60°C and it doesn’t even bother ramping up under full load under normal conditions. It does ramp up if the temperatures do get higher though if it’s hot in the room.

So I hope this clears things up a bit for you. In short: ignore idle temperatures and only get worried if you are hitting 70°C+ on the CPU cores. That’s all folks!

Windows 10 Crashing at Idle: Solved!
Trying out Amazon EC2!

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.