Strange phenomenon when experimenting with case fans

[B-Man13]

I just built a new system and have been experimenting with different settings. Here's the system I have.

CPU: E8400 clocked at 4GHz (445x9) w/ Vcore at 1.325v
Heatsink: Thermalright Ultra 120 Extreme w/ SilenX 120mmx38mm (90CFM)
Motherboard: Asus Rampage Formula
RAM: Kingstom HyperX PC2-8500 2x1GB (clocked at 890MHz and 4-4-3-11 timings)
Video Card: 2x Radeon HD 4850 in CrossFire
Hard Drive: Western Digital 300GB VelociRaptor
Blu-ray: LG GGW-H20L
Case: Antec Three Hundred
Power Supply: Antec NeoPower 650 Blue

The Antec Three Hundred comes with a 120mm rear exhaust fan and 140mm top exhaust fan There's a side vent for another 120mm fan and room for 2 front 120mm fans. I originally built this with only the rear and top fans. I installed the heatsink/fan to push air toward the rear exhaust. These were my temps running Prime 95 for a couple hours with room temperature around 76-78F:

CPU - 54
MB - 38
NB - 52
SB - 44
4850 - 71
HD - 29

I decided to add the 2 front intake fans thinking it would improve airflow. Doing this adjusted the temps as follows:

CPU - 53
MB - 41
NB - 55
SB - 48
4850 - 75
HD - 26

Interesting. Doing this actually made my temps go up by quite a bit (except the hard drive). So I turned the front fans around and made them exhaust, giving me 4 exhaust fans with air intake being the side vent (no fan). Now my temps looked like this.

CPU - 60
MB - 31
NB - 48
SB - 40
4850 - 69
HD - 32

All the chipset and system temps went way down and the CPU and hard drive temps went way up. I thought this seemed a little strange so opened the case and watched as the CPU temp came down to 53 and all the other temps jumped up another 4-6 degrees.

So now I need to decide which components I want to keep cool. I wanted to lower the NB temp to see how far I could push the FSB. When I tried doing a 533MHz FSB and setting the NB voltage to 1.55, the NB temp went up to 80. I don't really like the idea of my CPU running 6 degrees hotter though. What do you guys think?

 

[madcat20xac]

antec spotcool the nb

 

[houstonserenity]

Not sure if this will help with the 4850 but I used a PCI coolers to bring down my 8800 gt temps and it helped all my temps all around.


http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=40000573+4802&Description=pci+cooler&name=Top+Sellers

For 6 bucks x2 you cant go wrong

 

[RetiredChief]

Not really surprised at your results. Did some similar test on my system.
For a starter – Based on a MaxiumPC mag article about a yr ago, I tried using my front fans as an exhaust. Article indicated (They had some thermal imaging) that the front fans when used as intakes blew air across the HDD and picked up heat. This is true EXCEPT it (1) creates too great of a negative air pressure inside case and (2) reduces the air flow for the CPU because of (1) and the front fans are pulling air away from the CPU.

Rule #1 – You need to have exhaust equal to or just slightly greater than intake. DON’T forget to factor in PSU fan.
Rule #2 – Don’t position fans to fight one another

Here is what I found to work best on My system, Note - do not have top exhaust fan, wish I did:
Back – 120 x 38 mm exhaust. In addition to Top mounted PSU exhaust. Front a 120 mm intake.
Modified my side panel. Lower right (Front) 120 mm intake, Top left (Back) 120 mm exhaust

 

[B-Man13]

Thanks for the replies. I'm going to try a few more "positions" tonight. I'm trying to figure out why everything else gets cooler while the CPU gets hotter. When I put my hand near the side vent I can feel a lot of air rushing in. I think the air is hitting the video cards and motherboard then rushing toward the exhausts bypassing the CPU fan. I wonder if switching the CPU fan to pull air to the rear exhaust instead of pushing would help. there would only be an inch or less gap between the CPU fan and rear exhaust fan if I did that and may force the air through the TRUE.