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 Post subject: Can Rear case fan interfere with CPU fan?
PostPosted: Wed Nov 13, 2013 8:20 am 
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Joined: Tue Feb 21, 2006 10:28 am
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Location: austin,tx
Did a quick search but anyway,
If my audible rear case fan is under-volted, producing less CFM than the the CPU fan. 1) Does the rear case fan hinder CPU fan flow. 2) Would the CPU fan alone provide better exhaust out the back (over the VRM's). Is it better to remove the (only) case fan?

Note: The CPU and rear case fan are about 2" apart, in-line and blow rear. I like to think of the simplified version of two fans mounted at both ends of a tube (one with lower CFM).


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 Post subject: Re: Can Rear case fan interfere with CPU fan?
PostPosted: Wed Nov 13, 2013 10:10 am 
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It depends. There are many variables, like relative fan speeds, and whether there are other vents in the case nearby. I doubt the two fans give you much of a cooling advantage. It should like the CPU fan is mounted sucking air through the fins towards the back? You'd get more advantage mounting it on the other side blowing into the fins instead so you get a real push/pull effect with the 2 fans. Which cooler, CPU, case, fans etc?

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 Post subject: Re: Can Rear case fan interfere with CPU fan?
PostPosted: Wed Nov 13, 2013 3:03 pm 
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Location: austin,tx
MikeC wrote:
the CPU fan is mounted sucking air through the fins towards the back?
Thanks for he reply. The CPU fan pulls air through the cooler. The ram interferes with the fan when it's mounted on the other side.
MikeC wrote:
You'd get more advantage mounting it on the other side
Is it true airflow is also better on the fan's exhaust side (I remember something like that)? Anyway these sound like good reasons to find a way to do that.
MikeC wrote:
Which cooler, CPU, case, fans etc?
Going for a quiet PC sound system this time around: Core I5 2500k w/ full tower Gelid Tranquillo CPU cooler. A 120mm Nexus @12v is mounted to the cooler and another @7v is at the rear of the case. FIY I recently took out the front 140mm fan and HDD cages from the Lian-Li PC-6 case. There was little difference to the observable temps (don't know about the VRM's). Ordered an Accellero S1 GPU cooler with another Nexus 120mm for the Radeon 7870 (my Nvidia 570 died). So 3 active fans altogether not including the Seasonic 560 PSU fan which stays quiet.


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 Post subject: Re: Can Rear case fan interfere with CPU fan?
PostPosted: Wed Nov 13, 2013 10:35 pm 
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Location: Germany
CPU fan does not fit because of RAM modules with a big nonsense heat spreader i guess?

Sell the RAM and get low ones which do not interfere and solve your Problem by mounting the CPU fan as it is meant to be.

Setting the CPU fan @12v seems to high, but with the data supplied i cannot say any more.


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 Post subject: Re: Can Rear case fan interfere with CPU fan?
PostPosted: Wed Nov 13, 2013 10:50 pm 
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iirc, the Tranquillo samples we encountered had convex bases, not great for heat transfer. You could try lapping the HS, using a fairly coarse grade of sandpaper -- say 300? -- and finishing with perhaps 6-800. Also just remove the heatspreaders on the RAM. Most often useless. Done carefully, this is easy -- I've done it many times, as the RAM that goes on sale most often seems to be the ridiculously headspread type.

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 Post subject: Re: Can Rear case fan interfere with CPU fan?
PostPosted: Thu Nov 14, 2013 9:25 am 
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Thanks, the ram is standard Corsair. Actually i'm not worried about CPU temps right now as the cooler seems effective (45c max w/ prime 95). I would really, really like to take out the rear case fan though; especially if it contributes nothing (or hinders? cooling). Just a bit worried about the VRM's.

edit: I do have a temperature probe. Would simple contact with the VRM's provide a good thermal estimate?


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 Post subject: Re: Can Rear case fan interfere with CPU fan?
PostPosted: Thu Nov 14, 2013 11:03 am 
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Joined: Tue Feb 21, 2006 10:28 am
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Location: austin,tx
On second thought I'll find a way to go with the standard push-pull setup mentioned, and bypass these questions. Much easier and if the fans can run @ 7v I should be happy.


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 Post subject: Re: Can Rear case fan interfere with CPU fan?
PostPosted: Thu Nov 14, 2013 12:13 pm 
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picture_perfect wrote:
On second thought I'll find a way to go with the standard push-pull setup mentioned, and bypass these questions. Much easier and if the fans can run @ 7v I should be happy.

Good plan. Let us know how it works out.

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 Post subject: Re: Can Rear case fan interfere with CPU fan?
PostPosted: Thu Nov 14, 2013 2:30 pm 
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Joined: Tue Feb 21, 2006 10:28 am
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Location: austin,tx
Thanks, this site has been invaluable over the years.


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