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System vs. CPU temperatures

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libervisco's picture
Joined: 2006-05-04

I tend to get a bit paranoid every time when there is an incident with my computer which might imply the possibility of damage, especially if the computer is new, awesome and not so cheap.

In the interest of cutting down on noise I turned the smart fan option in my BIOS which is supposed to make the CPU fan spin only when it detects higher temperatures. After setting it that way it seems to have been working for a while and I forgot about it until last night when my computer shut down by itself a couple of times.

Second time, when I was working on it, I tried to turn it immediately on after sudden shut down and a few times after pressing the power button it turned on for a second and then turned off. This hinted me at temperature problems. And indeed, after finally turning it on, looking at the BIOS revealed a system temperature at above 80 degrees celsius, but falling.

Now, since I never was sure if the system temperature, for always being bigger on my comp than a CPU temperature was really system temperature. If it was the other way around then what I just saw was a temperature of my CPU - above 80 degree! That started my paranoia and prompted some research of the issue.

So to cut the story short, what I found out is that the way it was showing temperatures is correct. Indeed, system temperature is much higher than CPU. It is likely that the sensor is placed in some hotspot within the system (I couldn't find the sensor's exact location) whereas apparently well cooled CPU enjoyed much more comfortable temperatures. Still, I don't trust the smart fan and I wont use it again. The fan is spinning all the time now. What happened yesterday is most likely that the CPU reached 60 degrees (which is within the tolerable limits before getting damaged) and hence triggered a BIOS alarm (as it was set that way) which apparently resulted in shut down. The system temperature was about 80 because there is apparently a dependency between how hot is the CPU and how hot is the spot in which the system sensor is.

Reason why I believe CPU really is cooler than system temperature is because, for one, I couldn't make a mistake of switching connectors as I initially thought I did because there are no temperature related connectors. And second, I today started OpenArena and payed attention to the temperatures. temp2 spiked from 21 to 28 while temp1 remained at 41. Logically, the temp2 is then the CPU. Smiling

So now I'm wondering about two things. First, is anyone else having their system temperatures detected as higher than CPU? Second, where the heck are these sensors placed anyway? I couldn't find them (and they're apparently very small)? I have an additional sensor hanging on a wire that came with the case and it is plugged to the blue LCD on the case. I can position it anywhere in the case and it shows around 34 degrees right now (placed around the area close to the CPU fan).

Ah.. sorry this turned out to be such a big post.


Joined: 2005-12-20
You have to be really

You have to be really careful with system temps Smiling

I know it sounds weird, but unless you have a *really* good cpu fan, its not going to be 28 degrees under load during a game. That sounds like a sensor that is not on the CPU. I would advise you keep your CPU fan on at all times Smiling Especially in the summer. You dont want your computer to die now Shocked

libervisco's picture
Joined: 2006-05-04
From what I understand the

From what I understand the sensor is right below the CPU. Anyway, I didn't have the game on for long so the temperature would probably go over 30 if I were playing more. I'll check it out again later.

The fan is a stock one that comes with Core 2 Duo. Some say it's crappy, but compared to any others I've seen or had before, it seem quite great to me. It has both ridges for passive cooling and a fairly big fan.

In any case I will keep my fan on all the time now. I am making this my holy commandment. No more messing around with things in BIOS that think they're "smart" while they're not. Sticking out tongue

But I don't think the real temperature of the CPU went much above 60 yesterday while the operational maximum is I think somewhere around 70 or 75 so it can't possible be damaged by that.

As for system temp.. people say those can't be trusted, but I find it perfectly plausible for them to be big, yet not so damaging if the sensor is placed where the heat from the CPU dissipates on its way out the case (heating both the air and the sensor on the way).

tbuitenh's picture
Joined: 2005-12-21
Two things: One of the two

Two things:

One of the two sensors could be broken and read a higher or lower temperature than the actual.

Maybe the system sensor is placed close to the video card, which is also likely to become warm when playing a game. If you want to be sure you're only heating the CPU, try making an infinite empty loop, for example in python:

you@yourbox:~ $ python
>>> while True: pass

Note you need to hit enter twice after pass, otherwise python will still be waiting for input and the CPU won't get a workout. Stop it with control-c and exit python with control-d

libervisco's picture
Joined: 2006-05-04
Broken sensors on a brand

Broken sensors on a brand new motherboard. I don't even want to consider that option! :S

I did the loop and although it is happening very slowly the temp1 (one which I believe is the system) went from 39 to 40 and stopped there (I just turned the computer on and it usually does settle around 40). Temp2, however seems quite dynamic. It shows a temperature a degree higher for a second until it fully surpasses it and starts passing to even higher. But after a few minutes of running the loop it went from 27/28 to, as of now, 32/33. Temp1 is still on 40.

So I suppose that would indicate that the lower one indeed is CPU, right?

It could be the *system* sensor which is near the video card and hence so hot. Or it could simply be somewhere else where the heat exhausts are going over. In any case I don't worry so much about the system (environment) temperature being high because chips themselves are likely to be lower since they don't work as much as CPU. As long as CPU is cool and system isn't more than 50 I'm ok with it.

Edit: As I interrupted the loop Temp2 immediately jumped back to 28, and falling down.. 26/25..

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