[ale] cpu heat

[Jeff Hubbs]

Is that the CPU reading or the mobo reading (some mobos have sensors for 
both).

118F is what I would call on the high side.  These days, CPUs run hotter 
and hotter as a function of clock speed, then there will be a jump of 
some sort (CPU power dissapation improvement) that changes things for 
the better and then the temps ramp up again.  

Here's basically what ought to be happening.

The CPU itself needs a good heatsink and its own fan.  There also needs 
to be a good thermal interface between the CPU and the heatsink, in the 
form of thermal grease or thermal tape.

I once worked on a machine brought in by a client and was getting quite 
frustrated because the NT install would hang at nearly the same place 
every time.  After talking to the mobo mfr, I decided to check that 
thermal interface and sure enough, whoever put the machine together left 
the backing paper on the thermal tape on the underside of the heatsink, 
forming a nice layer of insulation and letting the CPU heat up to the 
not-gonna-work-at-this-temperature point (albeit not quite to the 
you-just-bought-yourself-a-1-GHz-key-fob point).  Removed the paper and 
the ruined thermal tape, replaced the tape with grease, and we were off 
to the races (saved about two days minimum on the project, too).

Once the thermal interface, the heatsink, and the fan are accounted for, 
there's still the issue of getting cool air to the heatsink in the first 
place.  

Hot air wants to rise, so don't fight that.  Also, your power supply, 
which is going to be mounted high in the case most of the time, 
typically will have a fan that's configured to blow OUT.  Don't fight 
that either.  You're going to want to encourage air to enter from the 
bottom and leave through the top, which is what convection would do if 
you used no fans at all (which you shouldn't do).  Some cases do this by 
letting you put exhaust fans in the upper rear and an intake fan in the 
lower front, which has never made sense to me because you've got more 
air leaving via fans than coming in via fans, such that pieces of dust 
that go meandering by your floppy drive are liable to make an unexpected 
trip into and through it, provided they don't land on other pieces of 
dust that stayed for the atmosphere.  Air that comes cruising into the 
case by way of the drive openings, spaces between drive bay covers, etc. 
don't do a lot for your CPU because it misses the CPU completely on the 
way through.  

I advocate having a positive-pressure case, with intake fans in the 
lower front.  This does two things for you:  it authoritatively puts 
cool air into the case right where it needs to be to mix it up with the 
CPU heatsink and fan, and you can filter that air first if you so desire 
(and I do).  The Antec case that I picked up from CompUSA has snap-in 
receptacles to put two fans in either the lower front or midway in the 
back; I chose to stick them in the lower front and leave the holes in 
the back open.  I got some air register filters (thin polymer mesh about 
11"x5") and attached squares of it to the front of the case behind the 
plastic cover with magnet tape.  

One thing that bothers me about some cases is that the fan mounting 
points are severely blocked by metal.  I have one full tower case - one 
that takes two fans in the upper rear - that was like that and it looked 
like over half its fan area was blocked.  I cut the excess metal away 
with a Dremel cutting wheel.  

You can get into the game with water cooling for around $120-150 for a 
complete kit.  I never went that route but if I did, I was going to take 
that full tower case I mentioned, cut a hole for the radiator in the 
top, and make an airbox out of sheet aluminum such that fans blew air IN 
from the upper rear and out the top through the radiator.  If I did 
this, though, I would have had to make a "stack" for the power supply 
exhaust fan lest hot air from the PS got sucked through the radiator. 
 If I had taken this route, I probably would have incorporated a chipset 
cooler as well.  

If you want to see what people are doing along those lines, go to 
www.overclockers.com.

- Jeff



Stephen Turner wrote:

> i just realized i dont know the range of heat a processor is supposed 
> to be in, i mean, i just got a new board and its hitting 118f and i 
> get scared (heard its not supposed to get over 101) and turn the comp 
> off, is this too hot? what is too hot? thanks for your time and help :)
>
>
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