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Why aren't my top fans affecting my CPU temp

Last response: in Systems
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November 19, 2011 4:17:17 PM

I've added two top Cooler Master Turbine Master Mach 1.8 fans as top fans for exhaust. I'm using the following system:
Case: CM 690 II Basic.
CPU heat sink: Cooler Master Hyper 212+.
Core i7 2600K - no overclocking yet. I want to but first want to make the system run cooler during summer.

I've also changed the standard rear exhaust fan for another Turbine Master Mach 1.8, setup as exhaust. My problem is that there doesn't seem to be any difference between having the two top fans on or off. CPU temperature and fan speed remain the same.

CPU heat sink is mounted so that it blows air from the front to the back of the case.

Does anyone have a suggestion as to why this is happening?

Silly ones out of the way: the fans are definitely blowing OUT of the top. Both fans do work when switched on.

Thanks in advance for suggestions and advice.

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a b B Homebuilt system
a c 215 à CPUs
November 19, 2011 4:18:41 PM

What are your temps at? There is a limit to how low you can get your temps since your heatsink works on a temperature differential and if you case temp is basically ambient temp you are as low as you can get it and adding more fans will never help.
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November 19, 2011 4:27:00 PM

Ambient temperature is about 30 degrees mid-day. Today's testing was only with 50% CPU load but CPU temperature staid at about 54 degrees celsius whether the top fans were on or off. I was expecting that, with the top fans on, I'd at least see the CPU fan RPM decrease a little, but no change there (stayed at about 1600 RPM).

Am I expecting too much with such a low CPU temperature at the moment. Sadly, my CPU load depends on the simulation I'm running at the time.
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a b à CPUs
November 19, 2011 4:38:11 PM

The case fans are designed to remove warm air from the case and bring cooler fresh air into the case. They won't have a major effect on your CPU temp. That is done by the heatsink/fan on the CPU itself. The bigger the heatsink the better cooling you get, as a general rule. The CPU temp will run 10-15C higher even when just surfing.
54C is OK for 50% load.
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November 19, 2011 4:43:30 PM

Just tested again, this time with IntelBurnTest using maximum stress level - 100% CPU load. With the top fans off, the CPU temp gets to 61 degrees celsius, CPU fan RPM 2070. With the top fans on I get 59 degrees and 2000 RPM now. Ambient temperature right now is about 27 degrees. Fantastic change. Sarcasm aside, is that really all I can expect at these temperatures? Will I see a larger drop in CPU temp when the ambient temperature starts getting to 33 - 35 degrees?
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a c 122 B Homebuilt system
a c 172 à CPUs
November 20, 2011 2:23:05 AM

If you really want to use the top fans, you should reorient the cooler so the cooler fan blows upward. Then test.

If the temps are a little better, try turning off the upper rear fan. It may be interfering with the airflow generated by the top fans. Use which ever gives you the better temps.

DelroyMonjo said:
They won't have a major effect on your CPU temp.

Not entirely true, Delroy. Once you remove the heat from the CPU, good airflow through the case will remove that heat. Otherwise, all you are doing is recirculating the heated air as it builds up inside the case.
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November 20, 2011 4:22:20 AM

also keep in mind that if you are exhausting air much faster than your case can bring fresh air into the case you arent helping... the air in the case essentially absorbs the heat produced by the cpu & components so if you are sucking it all out too quickly the air cannot absorb any heat to dispel. its called negative airflow. your temps arent really too bad though.
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November 20, 2011 11:29:39 AM

@jsc: Thanks. I'll dive in again in the next heat wave if I don't see any benefit when it gets that hot.

@AutoOrdnance: Shouldn't air absorb heat at a similar rate whether its being sucked out faster or slower? I'd expect the temperature of the air to affect how much heat gets absorbed? Having positive pressure seems to increase temperatures slightly anyway - only about 1 degree so I can hardly call it conclusive though.
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November 27, 2011 8:13:38 AM

Follow up: no heatwave and still no benefit from having the top fans. Thanks hunter 315 and jsc for the advice.
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November 27, 2011 8:21:05 AM

Best answer selected by chippies.
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December 6, 2011 9:12:32 AM

Follow up: Stressing both the GPU and CPU today has shown where the real benefit of the top fans lies: keeping the GPU cooler. CPU temperature only goes down by 1 or 2 degrees but the GPU's temperature drops about 5 degrees. At least there's some benefit to those fans :)  Today's test: Folding @ Home and Boinc, ambient temperature about 28 degrees.
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December 6, 2011 9:26:58 AM

Turn the top fans upside down forget every body elses moto of the exshaust fans, give this a try then post your readings. Think of it like a cooler the more cold air being sucked in a forced inside the case the better its not gonna lower your cpu temp if you dont have anything cold going in, theres nothing for all of those exshaust fans to remove i stick to one exhaust and one exhaust only on the rear with all my other fans blowing down onto the heatsink.
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