Why do temps increase when I turn my case fan on ?

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Why do temps increase when I turn my case fan on ?

Postby qqqq » Thu May 30, 2002 7:59 am

Enlight 7237 case
AMD 1.4 t-bird
Giga-byte GA-7DXR mobo (bios ver. f7)

I have 1 fan at front of case bringing air in
1 fan at rear of case exhausting air
PSU obviously exhausting some air too

I installed a 120 mm fan on the side of the case to blow air directly onto the mobo to help cool the CPU and system chip. Running some 3d games heats things up a bit. Stock HSF on the cpu also. I put some arctic silvr II on the HSF and it lowered temps 2C.

I have a Rheobus installed to control the rpm of my fans and it works good.

My problem is, when i turn on the 120mm fan, my system and CPU temps rise about 3c. I'm monitoring the temps after using the computer for varoius tasks, gaming, word, etc. from bios. After putting a load on the computer in some graphics intensive games, my CPU reaches 51c. When i turn on the 120mm, my cpu temp rises to 53-54c/system temp rises to 34c. I turn off the 120mm and my cpu drops to 50c/system 29c.

I havent tried turning the 120mm around to exhaust air but i thought blowing air directly onto the mobo would help cool things down. theres no room on the rear to add another exhaust fan. Do you think maybe im putting too much air into teh case?

When i turn off the rear fan and front fan and only have the 120mm blowing in, my temps still rise.

I await ur reply

Joe
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Postby Tolemac » Thu May 30, 2002 10:29 am

It will depend on where exactly you have the fan set up. It seems to me to be blowing air into the wrong spot, and it's defeating the purpose of the heatsink and the other case fans. You may want to try an 80mm fan instead of the 120mm, or you may want to put a rheostat on that fan and then adjust the speed till you get a the proper results. 8)
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Postby len444 » Thu May 30, 2002 5:22 pm

:arrow: :idea: add another exhaut fan at rear or top of case (if comfortable w/ mods- assumed you mod'd the case- tape off plastic bag around top of case inside, wider than new opening, then cut out opening- keep vibration to a minimum, or remove components to protect from damage). you will also want to check direction of air flow- think the case suffers from an imbalance- needs another exhaust fan!

http://www.tweak3d.net/tweak/airflowtweak/
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Postby ThEvil0nE » Thu May 30, 2002 5:46 pm

What I think you have is a bad case of "vacuum effect". This occurs when you have poorly placed fans and/or uneven intake and exhaust going on in that case.

Here's a question too folks...would a powerful 120mm intake fan blowing in and directly to the motherboard cause the fans on the mobo to act funny like rotate slower or something because of the strong air blowing to it (cpu fan and any other heatsink/chip)? :roll:
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Postby qqqq » Fri May 31, 2002 7:36 am

Could be the vacuum effect. I have a rheostat/rheobus hooked up and have full control of my fans rpm's.

I havent tried a lower rpm on the side 120mm fan. Ill try that and post the results.

Also, I'll turn the 120mm fan around to exhaust air out and post them results.

Joe
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Postby len444 » Fri May 31, 2002 8:34 am

:arrow: :idea: if the airflow of hsf is in the same direction as side fan, than more than likely ok, but if it (cpu fan) uses a vacuum to draw the heat out, then you'd have a problem, it could be turbulance from fan (cavitation/ vortices) disrupting airflow- but more than likely just an imbalance of more in fans than out- if you can add another out fan, that will probably remedy the situation!

:idea: [try adding baffles that deflect air downward slightly, say a piece 1/8" aircraft/poplar plywood- square, cut out opening (round) same as fan opening, and make vanes 5/8"x say 1/2" wider on each side of fan opening- same as width of square cut out, and place 6 vanes w/ equal spacing angling away from cpu- glue in place w/ ca glue and kicker (just for immediate contruction, can hold w/ hand and glue will setup rapidly) do fillets as well, secure w/ small bolts through ply and fan mounting holes. (a variation would be to rotate the baffles 90deg to rear of case, or better would be 45deg to rear/up of case, as downward baffles might cause a whirlpool effect in the case in the region at side fan and below to bottom of case)].
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Postby qqqq » Sat Jun 01, 2002 8:21 am

The 120mm fan was bringing air into the case. The HSF on the CPU was blowing air onto the cpu (same direction as the 120mm fan). That is why I was surprised the temps increased when I turned on the 120mm

I reversed the 120mm and have it exhausting air now. Since i have it controlled by a rheobus, I have the 120mm spinning at 1/2 its rated rpm. Now my cpu temp is back to where it was before I installed the 120mm fan.

I guess theres no substitute for a GOOD QUALITY HSF for teh CPU.

thanx for all your suggestions tho

Joe
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Postby len444 » Sat Jun 01, 2002 11:55 am

:arrow: :?: :!: you've got to have some serious restrictions on air flow as the cpu temps are the same w/ fan reversed (as w/o 120mm fan), and higher blowing into the case. is this your case?

http://www.newegg.com/app/Showimage.asp

:?: if the frontholes shown are the only air inlet then your going to have to bore them out to a larger size- say 1/4" (still will be restricted, though less)

:!: :idea: if i were you, i'd add a second exhaust fan, say to the top of the case (fan w/grill)- i'd remove the mb, and tape off a plastic bag right under the top of the case, which will contain most metal debris.

:arrow: :idea: if the side fan is right over louvered slots at side of case, i'd try to tape off the rest of the opening to the side of the fan, orientate the fan to blow in- that way no air will come back out the slots right next to the fan, and should push out the rear and psu fan openings
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Postby qqqq » Sat Jun 01, 2002 1:08 pm

[quote="Len444"] you've got to have some serious restrictions on air flow as the cpu temps are the same w/ fan reversed (as w/o 120mm fan), and higher blowing into the case. is this your case?



Lenn,

My front fan is in the lower part of the case. it came with them puny holes drilled ito the front grill. I cut a hole in the case grill the size of the fan opening. No restriction at all. It is the stock fan that came with the case so it doesnt move alot of air but it is ok.

my rear fan is in the upper rear of the case. The case came with a slot there to mount an exhaust fan. I went 1 better and cut out the grill so there is NO restriction to the exhaust.

All my cables are tied off and tucked away so as to NOT interfere with the air flow. I was thinking of cutting out another hole in the front and adding aother fan or just letting the 120mm fan pull air in thru it.

I believe that my stock HSF is not up to the task of cooling beter than 50c. I'll probably get a aftermarket HSF. I just have to search carefully though, I have a gigabyte mobo and it is the smallest cpu die. Alot of HSf's wont fit on it.

Joe
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