New CPU fan not running fast enough

By gavilan
Jan 22, 2007
Topic Status:
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  1. I bought a new Cooler Master CPU heatsink and fan to cool down my cpu. Problem is, the fan is only running between 1000 - 1500 RPM's, which is enough to make the BIOS freak out and say that the fan is not running fast enough. I have monitored the CPU temperature and it isnt overheating yet but it is getting fairly warm (around 67 C)

    The other thing about this fan is it has a 4 pin power connector and my mobo has a 3 pin cpu fan header. The fan plug is keyed so that it'll fit onto a 3 pin connector so i'm pretty sure it's connected properly.

    My question is does hooking the fan up to a 3 pin header have something to do with it running so slow and if it does is there a way to fix it so it runs at its rated speed?
  2. jb444

    jb444 Newcomer, in training Posts: 113

    I've never had a fan with 4 pin connector (I'm assuming you dont mean a molex connection), but check what each pin does by looking up your heatsink on the CM website (CM probably has good enough customer service to find out for you if you cant find the info on the web) and then check with your mobo manual its all connected right.

    Its not unlikely that the fan is faulty (just buy a new fan off newegg, or CM probably sell replacement fans for their heatsinks).

    Is 67C under load? Also which cpu do you have?
    If its Intel and 67 is load temp then I would leave it alone and simply disable cpu fan warning in the BIOS. (I have never needed my cpu fan above 1600rpm, even under load, so (depending on the heatsink) 1500 isnt incredibly slow.

    If the chip is AMD or that temp is idle or just under a small load and you definately have tried all the above (and any other suggestions made, I may well have missed somthing) then I would buy some AS5 and check the seating of the heatsink.
  3. KingCody

    KingCody TechSpot Guru Posts: 1,568   +7

    since most people just use the stock heatsinks that come with the processors, most BIOSes fan speed alarms are set by default to high speeds. you generally have to set that speed to a lower value or turn it off completely when you use an aftermarket CPU cooler.

    aftermarket coolers have more efficient heatsink designs than stock coolers, as a result the fans do not have to spin as fast to cool just as well. many coolermaster CPU coolers have low speed fans. what model cooler did you buy?

    fans with 4 pin connectors are called PWM fans (Pulse Width Modulated). they are designed to be speed controlled by the motherboard without lowering the voltage, which generates excess heat.

    The colors on a 4-pin (PWM) fan are not the same as a standard 3-pin fan. The "standard" wire colors for a 4-pin (PWM) fan are:
    • BLACK = ground
    • YELLOW = +12v
    • GREEN = speed sensor
    • BLUE = control (pulse signal)
    if you use a 4-pin (PWM) fan with a 3-pin fan header, then the un-used wire should be the blue wire

    When connected to a 4-pin fan header, the PWM fan speed is regulated by the motherboard via a "pulse" signal. in most cases, when connected to a 3-pin header the fan does not detect a pulse signal and simply spins at full speed constantly. however, on certain model PWM fans, connecting them to a standard 3-pin header causes the fan to run at it's lowest speed instead.

    :wave:
  4. gavilan

    gavilan Newcomer, in training Topic Starter Posts: 136

    The fan / heatsink I bought is a CoolerMaster Hyper 48. It says on the box that the fan speed varies from 1400 - 3200 RPM (Controlled by PWM) which would be the unconnected blue wire you were telling me about.

    I'm running a pentium 4 3.0E Prescott OC'd to 3.3 GHz. 67C is about what it averages at max load; I've measured it while gaming and video encoding.

    So far my system has been running stable. The heatsink is very secure and it's bonded to the chip with AS5.
  5. tweakboy

    tweakboy TechSpot Maniac Posts: 518

    Thats a very slow speed for a cpu hsf,

    I bet the max speed is 3000rpm at least,

    What did the specs say on that cooler ?
  6. gavilan

    gavilan Newcomer, in training Topic Starter Posts: 136

    It says on the box that the fan speed varies from 1400 - 3200 RPM (Controlled by PWM)
  7. tipstir

    tipstir TS Ambassador Posts: 4,487   +73

    You can bypass that connection and use more of the PSU for power, though the FAN will always be on as it should. You should not get more RPMs out of it. There should be connectors you can use or buy online or even make to support this new type of connector.
  8. KingCody

    KingCody TechSpot Guru Posts: 1,568   +7

    gavilan,

    when i posted earlier, i edited and accidentally deleted the last part which stated: "on certain model PWM fans, connecting them to a standard 3-pin header causes the fan to run at it's lowest speed" (i fixed my above post)

    It would appear that you have one of the PWM fan models that defaults to it's lowest speed when connected to only 3-pins (which unfortunately is no good for a hot-running Prescott CPU). I don't own a PWM fan, so I have never tried this but according to this article, you can simply bridge the yellow (+12v) and blue (PWM pulse) wires together to force the fan to run at full speed (which could then be controlled via lower voltage)

    -or you could replace the fan with a standard 3-pin fan instead ;)

    :wave:
  9. tweakboy

    tweakboy TechSpot Maniac Posts: 518

    Does it have the little 3 pin connector,, might have to conenct that to mobo as well,
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