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Push/Pull - No noticeable decrease in temperature?

post #1 of 22
Thread Starter 
So I've been messing around with fan configurations for the last couple weeks, and my results haven't been quite what I expected. For cooling, I'm using a Scythe Mugen 2, with two 120mm fans. My case has 120mm exhaust fans on the top and rear. All four fans are Scythe Slipstream 1900RPM. My CPU is a Phenom II X4 955BE at 4Ghz, 1.4 volts.

When I just have one fan blowing air across the heat sink towards the rear exhaust, with all three fans at 100%, temperature at load is around 50c, peaking at 52c once in a while when running Prime95 for 2-3 hours. Idle temperature is 35-36c.

When I add a second fan for a push/pull setup, with both fans running at 100%, the temperatures stay exactly the same.

If I move the second fan to the bottom of the heat sink, so that one fan is blowing across towards the rear exhaust, and the other is blowing up towards the top exhaust, the temperatures also stay exactly the same. (I didn't really expect this setup to have much of an effect, but I figured I'd try it.)

If I turn the speed of the second CPU fan up and down, it also doesn't seem to have any effect in either configuration.

I was expecting to see some change in temperature as I added/removed fans. Is the purpose of push/pull just to get air to the exhaust fans faster? Or should there be a noticeable temperature change?
    
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post #2 of 22
Well, it depends on the heatsink. Some heatsinks, like the NH-14 or Hyper 212+, are heatsinks where the air has only one way to go, and often needs a little help getting through it. Adding the second fan helps pull that air through. On the mugen II though, its fins, while having far more of them, are smaller, thus less drag, and more chances for the air to escape before it grinds to a halt at the core of the unit. If your temps are maxing at 52C no matter what you do, i would suggest you go with the quietest setup and enjoy. I dont see you getting much more out of that processor, and 52C full load is quite respectable, and on a single fan thats very nice. Testament to how good the mugen II is.

Some heatsinks are designed to benefit from multiple fans, whereas others have the option, but sometimes its not needed because one fan is more than enough.
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post #3 of 22
Check your thermal interface material for full coverage as well. If it dosnt have full coverage, it wont cool efficiently and effectively.
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post #4 of 22
Thread Starter 
I'm not too worried about the thermal gunk, I think I applied it correctly, since the temperatures seem pretty reasonable. I think I'll just take Cyrious' advice and stick with one fan, since it's quiet and the second fan has no appreciable effect.

Thanks guys.
    
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post #5 of 22
Well, with that particular fan I'm not surprised you see no differences in temps. From the testing I've been doing, it seems that a pull fan only really helps when you are using gentle fans. Try comparing a single Slip Stream 1200 rpm with two, for example. Or better: one 800 rpm vs two.

You'd be better off trying to reduce the number of fans you are using to get a quieter rig. For example, remove your rear fan and cut out that rear grill. Leaving a way for the air to leave quietly on its own allows you to use one less fan, for example.

BTW - do lubricate your Slip Streams before you commit them to steady use. The re-lube periodically, like your car. SS's have a reputation of breaking down that I think is lubrication related. See item 3 in my sig.
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post #6 of 22
Thread Starter 
Thanks for the advice. I actually stumbled across your post about lubricating fans the other day and lubricated all my fans as I was working today.

Noise isn't really a huge concern, my old computer was appallingly loud, so my current rig sounds like a gentle breeze in comparison. I'm more concerned about getting things as cool as possible, since I have no air conditioning in the summer.

Do you think that two gentler fans would be more effective than the single 1900RPM fan? Maybe achieve the same cooling with less noise? I think I have a couple of 1200RPM Slip Stream fans kicking around, so I will test those out tomorrow.
    
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post #7 of 22
I too added a second fan to my Mugen 2 for a push/pull setup and saw no real temperature decrease. Mine will actually level out around 56C under Prime at 1.425v
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post #8 of 22
High speed fans won't change the temperature. Push pull seems to be better for quiet, low speed fans. One good fan seems to be the best way to do it.
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post #9 of 22
i know on my rad, i only droped like 1*c adding push/pull and its alot noisyer
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post #10 of 22
have you considered a pull only setup? If you have good air movement through the heatsink, a pull setup might be beneficial for you.
Edited by Captain Mayhem - 2/23/11 at 11:24pm
    
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