Questions about CPU heatsink and reported temps BIOS vs OS

[Mikey-2-Guns]

I just installed a new heatsink fan combo because the stock one was having issues where the fan would not run sometimes.

I installed a new heatsink, one of the tower type ones with the fan on the side and direct contact copper pipes going to a large aluminum heatsink. When I installed it I looked at the temperature on the BIOS and it was hovering between 48C-50C. I installed two programs Core Temp and Real Temp and both of them are reporting 32-35C at idle. That's a pretty big difference and I was wondering if the BIOS could be reporting the temps wrong.

[AOD_Syph3n]

What processor are you running? Is it overclocked at all? And the obvious question, because we don't know your technical skills, the new heatsink is connected to the mobo at the CPU FAN connector? Does your BIOS provide an option for manually adjusting CPU Heatsink fan speed?

[ModJPB]

It is normal that the bios and and software program report two different temps but not as much as you are seeing. Have you tried seeing if your motherboard manufacturer makes a software to measure temp.

You could also put a load on the processor to see if it rises quickly so you can determine if the software is measuring the correct sensor.

[Mikey-2-Guns]

What processor are you running? Is it overclocked at all? And the obvious question, because we don't know your technical skills, the new heatsink is connected to the mobo at the CPU FAN connector? Does your BIOS provide an option for manually adjusting CPU Heatsink fan speed?

It's a i5 2500K sandy bridge, not overclocked except for the automatic turbo boost thing. I had the fan on the wrong direction, switched it and now it's reading around 45C in BOIS and 30-32C at idle in the OS and yes the fan is connected at the CPU fan plug. It says it's running about 1400 RPMS.

[Mokona512]

For most motherboards, they will report the temperature sensor readout from the thermal sensor on the motherboard, while most applications will use the thermal sensor built into the CPU.

for example using AIDA 64 will report both sensor readouts and the motherboard sensor can often be much higher as they often have an offset to account for the sensor not making perfect contact with the die of the CPU.

Some motherboards will also run all fans at their low speeds while in the bios because the CPU usage will be low.

[Mikey-2-Guns]

For most motherboards, they will report the temperature sensor readout from the thermal sensor on the motherboard, while most applications will use the thermal sensor built into the CPU.

for example using AIDA 64 will report both sensor readouts and the motherboard sensor can often be much higher as they often have an offset to account for the sensor not making perfect contact with the die of the CPU.

Some motherboards will also run all fans at their low speeds while in the bios because the CPU usage will be low.

OK, so for accurate temperatures the OS programs would be what to rely on? BTW what program is that you a running in the picture? Also for some reason the 4th core on mine seems to maintain substantially lower temperatures on load than the others. All of the cores don't get above 54C but for some reason the 4th never goes above 50C and will actually read 25-27C when I start to load a program.

[Mokona512]

I am using AIDA64

The CPU temperature, is pretty much the motherboards built in sensor, but for the temperatures labeled for each core, that is using the sensors built into the CPU which can be considered to be more accurate. The bios will often not read those sensors, thus making the applications in windows more accurate.

[Mokona512]

grrr annoying 5 minute edit time limit


For the 4th core being at a lower temperature, it can depend on the if that core is idle while others are being used, or it can be if the thermal compound id not evenly spread across he CPU, thus causing the area where the 4th core is located to have a little better contact with the heatsink. the only way to be sure is to fully load all cores and see if the temperatures level out. (you can do this by running a video encoder, or prime95, or repeated runs of cinebench.

prime95: http://www.majorgeeks.com/files/details/prime95.html

cinebench: http://http.maxon.net/pub/benchmarks/CINEBENCH_R15.zip

handbrake (video converter): http://handbrake.fr/