System vs. CPU temperature (7VAXP)

Archived from groups: alt.comp.periphs.mainboard.gigabyte (More info?)

The system temperature on my computer is always higher than the CPU
temperature. For example, the current CPU temp is 41.1C, while the system
temp is 47C. The relative difference remains constant even under load.

From a thermodynamic standpoint, is that even possible?

I asked GB tech support if the sensor display was reversed, and they
assured me that the temperature difference would be "normal if you got a
slower CPU and better heat sink fan."

I'm running an XP 2700+ (stock timings) with a CoolerMaster HHC-001 H/F on
a 7VAXP Rev 1.2. It's inside an Antec Sonata case (380W TruePower P/S)
with a 60GB and a 200GB hard drive. All three mem slots are occupied
(Kingston PC 2700 512 MB).

I've searched for an answer to this and gotten nothing but conflicting
information. Any help would be appreciated.

While I'm on the subject, how often should the H/F be reseated and thermal
paste reapplied? Two months ago, my CPU temp was 36C idle, and now it
idles at 40-41C. I work in a relatively dusty environment, so some of it
is attributable to dust accumulation. Should I be concerned about the idle
temp? Load temp now peaks at 48C CPU and 52C system.

Thanks in advance,
Orange Barrel
9 answers Last reply
More about system temperature 7vaxp
  1. Archived from groups: alt.comp.periphs.mainboard.gigabyte (More info?)

    On Tue, 20 Apr 2004 11:39:57 -0500, Orange Barrel wrote:

    >The system temperature on my computer is always higher than the CPU
    >temperature. For example, the current CPU temp is 41.1C, while the system
    >temp is 47C. The relative difference remains constant even under load.
    >
    >From a thermodynamic standpoint, is that even possible?

    No, that would be in conflict with one of natures most basic laws: the
    second law of thermodynamics. Heat always passes from a warmer body to a
    colder body.

    If your readings were correct, the surrounding air would actually heat up
    the CPU in stead of cooling it down, so you would be better off without a
    CPU cooler, which would only serve to speed up that process. Don't try to
    remove the cooler, though! :-)

    Something's wrong with your readings.
    --
    Best regards,
    Henrik Dissing

    (e-mail: hendis AT post DOT tele DOT dk)
  2. Archived from groups: alt.comp.periphs.mainboard.gigabyte (More info?)

    Orange Barrel wrote:
    > The system temperature on my computer is always higher than the CPU
    > temperature. For example, the current CPU temp is 41.1C, while the
    > system temp is 47C. The relative difference remains constant even
    > under load.
    >
    > From a thermodynamic standpoint, is that even possible?
    >
    > I asked GB tech support if the sensor display was reversed, and they
    > assured me that the temperature difference would be "normal if you
    > got a slower CPU and better heat sink fan."
    >
    > I'm running an XP 2700+ (stock timings) with a CoolerMaster HHC-001
    > H/F on a 7VAXP Rev 1.2. It's inside an Antec Sonata case (380W
    > TruePower P/S) with a 60GB and a 200GB hard drive. All three mem
    > slots are occupied (Kingston PC 2700 512 MB).
    >
    > I've searched for an answer to this and gotten nothing but conflicting
    > information. Any help would be appreciated.
    >
    > While I'm on the subject, how often should the H/F be reseated and
    > thermal paste reapplied? Two months ago, my CPU temp was 36C idle,
    > and now it idles at 40-41C. I work in a relatively dusty environment,
    > so some of it is attributable to dust accumulation. Should I be
    > concerned about the idle temp? Load temp now peaks at 48C CPU and 52C
    > system.

    I've had similar readings on my board (7VAXP Ultra), CPU temps (XP2800) were
    39º and system temps were 42º. However after making some changes to the
    case, adding soundproofing and ambient temps in this region have risen due
    to a change in season... CPU temps are now 45º, but system temps remain
    constant at 42º.

    This would indicate that there is something wrong with the readings I'm
    getting. I used to have an old Matsonic cheapo MB, and the system temps on
    that thing used to jump around between 30-50º, and the CPU temps always read
    56-58º, and upto 62º under load... I never believed them though, simply
    because after swapping the CPU and Heatsink into another board in an
    identicle case... case and cpu temps were 34 and 48º respectively... the
    same heasink in my other PC on a faster CPU gives an even lower 45º... and
    swapping heatsinks out for faster and more efficient ones (going from AMD
    standard HS (alluminium) to an all copper coolermaster Delta heatpipe, and
    then a coolermaster all copper aero 7) all gave identical temps... and
    there's no way on earth that that's possible.


    H
  3. Archived from groups: alt.comp.periphs.mainboard.gigabyte (More info?)

    Orange Barrel <lucy@in-the-sky-with-diamonds.net> wrote in message news:<pan.2004.04.20.16.39.53.429859@in-the-sky-with-diamonds.net>...
    > The system temperature on my computer is always higher than the CPU
    > temperature. For example, the current CPU temp is 41.1C, while the system
    > temp is 47C. The relative difference remains constant even under load.
    >
    > From a thermodynamic standpoint, is that even possible?
    >
    I think it is possible , rather very logical i would say from a
    thermodynamic and fluiddynamic point of view. That is because the
    processor has larger fan and it dissipates the heat away, but the hot
    air goes and stays around the system chip(northbridge) which has much
    smaller fan, and it is very near to the proccesor. Mine temperatures
    are about the same, and yes many times the system temperature can be
    up to 4-5 degrees higher(i have seen 48C CPU and 53 System after alot
    of gaming.)

    You dont have to worry about temperatures if they dont go much higher
    than 50C under load always. Of course the summer season you should add
    7-10C unless you have good air condition.
  4. Archived from groups: alt.comp.periphs.mainboard.gigabyte (More info?)

    On 23 Apr 2004 02:59:16 -0700, Dimitris wrote:

    >> From a thermodynamic standpoint, is that even possible?

    > I think it is possible , rather very logical i would say from a
    >thermodynamic and fluiddynamic point of view. That is because the
    >processor has larger fan and it dissipates the heat away, but the hot
    >air goes and stays around the system chip(northbridge) which has much
    >smaller fan, and it is very near to the proccesor.

    I suppose it comes down to what is meant by "system temperature". If it
    reflects the temperature of something which itself produces heat, such as
    the north bridge chip, you could be right.

    However, all the system temperature reporting motherboards that I have come
    about had a sensor mounted in safe distance from and significant heat source
    and did therefore give a good indication of the air temperature in case. The
    CPU temperature was always reported significantly higher than the system
    temperature.
    --
    Best regards,
    Henrik Dissing

    (e-mail: hendis AT post DOT tele DOT dk)
  5. Archived from groups: alt.comp.periphs.mainboard.gigabyte (More info?)

    Henrik Dissing <sorry@drowned.in.spam.invalid> wrote in message news:<sosk80d0nm5hhi10qqadilib4s7578tt7t@4ax.com>...
    > On 23 Apr 2004 02:59:16 -0700, Dimitris wrote:
    >
    > >> From a thermodynamic standpoint, is that even possible?
    >
    > > I think it is possible , rather very logical i would say from a
    > >thermodynamic and fluiddynamic point of view. That is because the
    > >processor has larger fan and it dissipates the heat away, but the hot
    > >air goes and stays around the system chip(northbridge) which has much
    > >smaller fan, and it is very near to the proccesor.
    >
    > I suppose it comes down to what is meant by "system temperature". If it
    > reflects the temperature of something which itself produces heat, such as
    > the north bridge chip, you could be right.
    >
    > However, all the system temperature reporting motherboards that I have come
    > about had a sensor mounted in safe distance from and significant heat source
    > and did therefore give a good indication of the air temperature in case. The
    > CPU temperature was always reported significantly higher than the system
    > temperature.
    Even if the system temperature isnt that of the northbridge chip, if
    the temperature sensor is located at a point with bad air flow(out of
    reach of external cool air), then heat leaves other components (cpu,
    hard disks) and is accumulated to that point(this can be done with
    internal flow patterns of hot air ).
    I believe that the system temperature is made up as an average of
    northbridge temp and another one or two temperatures sensors across
    the board, or maybe other important chips like southbridge. But
    because northbridge temp becomes high(due to the reason i mention in
    my first message), the average becomes also high.
  6. Archived from groups: alt.comp.periphs.mainboard.gigabyte (More info?)

    On 26 Apr 2004 04:29:12 -0700, Dimitris wrote:

    >Even if the system temperature isnt that of the northbridge chip, if
    >the temperature sensor is located at a point with bad air flow(out of
    >reach of external cool air), then heat leaves other components (cpu,
    >hard disks) and is accumulated to that point(this can be done with
    >internal flow patterns of hot air ).

    The point is that, at a certain point, heat will stop passing from the CPU
    and harddisks to that point with bad airflow.

    In a closed system, nothing can become warmer than the hottest heat source.
    You cannot accumulate heat just by not transporting it away, you need a heat
    source hotter than the current temperature.

    The temperature of that point with bad air flow will never become hotter
    than the hottest of the heat sources in the cabinet, which is likely to be
    the CPU.

    I'm sorry, but what you propose is physically impossible.
    --
    Best regards,
    Henrik Dissing

    (e-mail: hendis AT post DOT tele DOT dk)
  7. Archived from groups: alt.comp.periphs.mainboard.gigabyte (More info?)

    Henrik Dissing <sorry@drowned.in.spam.invalid> wrote in message news:<f7vp809cc8ngucqnfjtfb7g38i2ap46cjt@4ax.com>...
    > On 26 Apr 2004 04:29:12 -0700, Dimitris wrote:
    >
    > >Even if the system temperature isnt that of the northbridge chip, if
    > >the temperature sensor is located at a point with bad air flow(out of
    > >reach of external cool air), then heat leaves other components (cpu,
    > >hard disks) and is accumulated to that point(this can be done with
    > >internal flow patterns of hot air ).
    >
    > The point is that, at a certain point, heat will stop passing from the CPU
    > and harddisks to that point with bad airflow.
    >
    > In a closed system, nothing can become warmer than the hottest heat source.
    > You cannot accumulate heat just by not transporting it away, you need a heat
    > source hotter than the current temperature.
    >
    > The temperature of that point with bad air flow will never become hotter
    > than the hottest of the heat sources in the cabinet, which is likely to be
    > the CPU.
    >
    > I'm sorry, but what you propose is physically impossible.

    You forgot the fans. They blow air and remove the heat from the cpu to
    other points in the internal of the case. So things like what i
    suggest can happen. Your view of the situation is rather simplistic
    i.e two points A and B , A is hotter, B is cooler, and B no matter
    cant become hotter than A. If you have a device which with mechanical
    work transfer heat, then anything can happened, like transferring heat
    from a hot to a hottest. This is physically possible and in accordance
    with the 2nd thermodynamic law. Also you tried to view only by
    thermoquasistatic-dynamic point of view. You forgot the fluid dynamic
    point of view(fans and forced airflow regardless of temperature
    difference.)
  8. Archived from groups: alt.comp.periphs.mainboard.gigabyte (More info?)

    The system temperature is measured on the Northbridge with a VAXP. My sys
    temp always runs lower than the CPU temp. I can't understand how the sys
    temp could be higher. Use that as a relative temp and if it starts to get
    unstable or averages higher over time, then I would be concerned.


    "Orange Barrel" <lucy@in-the-sky-with-diamonds.net> wrote in message
    news:pan.2004.04.20.16.39.53.429859@in-the-sky-with-diamonds.net...
    > The system temperature on my computer is always higher than the CPU
    > temperature. For example, the current CPU temp is 41.1C, while the system
    > temp is 47C. The relative difference remains constant even under load.
    >
    > From a thermodynamic standpoint, is that even possible?
    >
    > I asked GB tech support if the sensor display was reversed, and they
    > assured me that the temperature difference would be "normal if you got a
    > slower CPU and better heat sink fan."
    >
    > I'm running an XP 2700+ (stock timings) with a CoolerMaster HHC-001 H/F on
    > a 7VAXP Rev 1.2. It's inside an Antec Sonata case (380W TruePower P/S)
    > with a 60GB and a 200GB hard drive. All three mem slots are occupied
    > (Kingston PC 2700 512 MB).
    >
    > I've searched for an answer to this and gotten nothing but conflicting
    > information. Any help would be appreciated.
    >
    > While I'm on the subject, how often should the H/F be reseated and thermal
    > paste reapplied? Two months ago, my CPU temp was 36C idle, and now it
    > idles at 40-41C. I work in a relatively dusty environment, so some of it
    > is attributable to dust accumulation. Should I be concerned about the idle
    > temp? Load temp now peaks at 48C CPU and 52C system.
    >
    > Thanks in advance,
    > Orange Barrel
  9. Archived from groups: alt.comp.periphs.mainboard.gigabyte (More info?)

    "guym" <nada@nada.net> wrote in message news:<MK2dndJLu8k7RiXdRVn-sA@gwi.net>...
    > The system temperature is measured on the Northbridge with a VAXP. My sys
    > temp always runs lower than the CPU temp. I can't understand how the sys
    > temp could be higher. Use that as a relative temp and if it starts to get
    > unstable or averages higher over time, then I would be concerned.
    >
    >
    It depends on which is your cpu, and how good the cpu fan is. A better
    fan removes the heat from the cpu and spread it to other components in
    the system, and the northbridge is the most likely to be affected, and
    the one getting the biggest portion of that heat.

    To clear it up i will speak with concrete numbers and give a more
    detailed analysis. Say that your CPU temp is about 48C.. This means
    that the air above the cpu fan has, on average, somewhat lower
    temperature than 48(say 45), and the air after passing through the cpu
    heatsink about equals that of the cpu(48C). Now because of the big
    airflow that the cpu fan induces, this 48C temp air will dominate the
    area above the northbridge fan. Now the amount of heat per second
    removed from the northbridge chip is proportional to the temp
    difference of the air above and under the fan, and proportional to the
    quantity of air that passes through, per second. Since the latter
    quantity is small(cause of the small northbridge fan) we can say that
    almost solely depend on the temperature difference.. Since the temp is
    48C above the northbridge fan, after blowing and passing through the
    northbridge heatsink, the air temperature goes a bit higher than
    48C(How much higher depends on the quantity of airflow/sec that passes
    through, hence on the fan size,rotation speed e.t.c). But the
    temperature of air that leaves the northbridge heatsink(which is as
    explained before a bit higher than 48C) about equals that of the
    northbridge chip. Hence the temp of the northbridge chip is a bit
    higher than 48Ci.e a bit higher than cpu temp.

    Now where this analysis goes wrong in your case so that you always
    have lower system temperature. Simply you must have better ventilation
    in the case so that most of the hot air from cpu goes outside and
    doesnt dominate the area above the northbridge fan.
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