Stupid Newbie Question - Why is CPU temp less than ambient?

[Borin]

Hello everyone; this is my first post. I am brand new to overclocking. I have been tossing around the idea of upgrading my CPU for a while now (I have FX6300), but quickly discovered the FX8350 is the only drop-in upgrade I can put in my board (not enough MB power for 9590). So instead of shelling out for a new MB as well, I figured I'd try OC'ing for fun. If I fry the thing, I'm no worse off since I was thinking about upgrading anyway.

Anyway, to get started I picked up a Noctua DH-15 and managed to stuff it into my case with a bit of banging on the side panel. On the stock cooler I ran around 28-30C idle, and on the Noctua it now jumps around 17-22C idle. This confuses me though, because the ambient temp is 25C. This just isn't possible...how are my temps being reported this low, and should I stop trying to push the CPU if I can't get accurate temp readings?

All I've done so far is change the multiplier, and disabled the PWM stuff. The basic idea is keep increasing the multiplier until unstable, then increase the voltage to compensate, yes?

Thanks for reading my ramblings.

CPUz / HWINFO:

Spoiler

 

[Blaylock]

Welcome to the Forum Borin!

Ah this brings back memories to my first post. Same issue. Here have a read at the first few posts and see if they'll work for you too.

http://www.overclockers.com/forums/...H-CRAP-quot-Core-temp-not-displaying-properly

 

[EarthDog]

Welcome!

Quite simple...because its reading inaccurately. The sensors are not accurate on idle but get more accurate on load.

 

[trents]

Just like you can't expect to accurately weigh a box of feathers with a semi truck scale because it isn't built to accurately weight light objects. Temperature sensors on motherboards and in CPUs are designed to protect against overheating, not to give accurate temps at idle.

 

[Borin]

Good to know, thanks for the information guys. I have another question. In the snippet I posted above, in the HWINFO screenshot, there is a temp listed for CPU0 at 17.6C...this I'm assuming is the actual CPU. Then below that is a temp for CPU, under the heading ASUS M5A97, of 36C. What is this...is it my NB? What is an acceptable limit to keep this under?

 

[trents]

I think CPU and CPU0 are the same sensor being read which is on the processor die.

In the section below that where you CPU temp as 36c that is probably your socket temp.

 

[chrisjames61]

Just like you can't expect to accurately weigh a box of feathers with a semi truck scale because it isn't built to accurately weight light objects. Temperature sensors on motherboards and in CPUs are designed to protect against overheating, not to give accurate temps at idle.

That is a very good analogy. Best I have heard yet explaining this question.

 

[RJARRRPCGP]

Welcome!

Quite simple...because its reading inaccurately. The sensors are not accurate on idle but get more accurate on load.

Yep, even though it don't get stuck. OTOH, some 45 nm Intels won't go below 45 C or close to there..... Going by the forum posts, the AMDs seem to do the same thing as 65 nm Intels, show an impossibly low idle temp, but that may be due to wrong setting in the program, like with 65 nm Core2s.....