XP-90 or 120 Blowing Up - Affect on System Temps?

dfrost · Post by **dfrost** » Fri Apr 15, 2005 4:23 pm

Now that I've got the S12 sucking out air just above the CPU, and the Sonata exhaust next to it doing the same thing, it seems like an up-blowing XP-90 or 120 could really improve airflow around the hot end of the motherboard. Any Thermalright users that can comment on that?

Checked back in the archives and one SPCR'r claimed a few degrees cooler with his XP-n sucking air up through the fins. I re-read the reviews and looked at the temp differences up versus down (slight benefit down), but those tests were done outside a case with no adjacent fans.

I wonder about the related temperature effects on the surrounding heat sources - NB, MOSFET's, my passive VM-101. Would the XP-120 be superior to the XP-90 because it's pulling air from a larger area?

Yes, I've read the forum questioning the PSU as heat evacuator several time. But dang, that Seasonic works great and quietly.

Side Note: These forums (and the projects they motivate) are seriously addictive. A few months ago, I hadn't even opened my Dell case for the first time. Now I'm trying to develop the next fun quieting/cooling project before the AS5 has cured from the last one (replaced and isolated the 7000B fan).

Tibors · Post by **Tibors** » Fri Apr 15, 2005 6:27 pm

There is two things to consider.

One: When blowing down, the voltage regulators and the memory get additional cooling, which doesn't happen when blowing up.

Two: The reported differences (if they existed) were marginal. So why bother?

Now if you have a Dell, so probably no temp sensors, else this was one of the easiest mods to test.

mathias · Post by **mathias** » Fri Apr 15, 2005 6:50 pm

Tibors wrote:One: When blowing down, the voltage regulators and the memory get additional cooling, which doesn't happen when blowing up.

Are you sure? They have to get at least some airflow from a fan pulling air away, plus a downward fan would be blowing air already heated by the CPU.

m0002a · Post by **m0002a** » Fri Apr 15, 2005 8:13 pm

Has anyone actually considered trying it, rather than speculating about the theory? Given that the Thermalright XP fans are held on with clips, it is very simple to flip it and see what happens.

Regarding memory, if you only have two stick of RAM, most of the time you use slots 2 & 4, or 3 & 4 (depending on which board) and still get dual channel memory access. Using slot #1 puts the memory very close to the heatpipes on the XP-120, so if you move them over a bit it is probably better than having a small amount of air on them (on most boards the XP-120 fins are parallel to the DIMMS, so they would not get much airflow anyway).

dfrost · Post by **dfrost** » Fri Apr 15, 2005 8:51 pm

Tibors,

Sorry if my side note threw you off. Reference to the Dell was my old, pre-SPCR PIII system. Current is my sig system, P4 in a Sonata, etc. with a bunch of those fun cooling, quieting mods in place. I measure temps and fan speeds with Abit's uGuru and Speedfan.

Being the inveterate test engineer, I'd greatly appreciate it if someone would try inverting the air direction. Otherwise, I'll just be forced to go with an XP-n myself to get more data!

el_ · Post by **el_** » Fri Apr 15, 2005 9:05 pm

if the ihs isn't epoxed you could take that off and clean/lap the core. I think that the 3.0ghz isn't epoxied but some of the newer heat spreaders are so don't try it unless you are sure.

As far as teh 90/120 question? It only helps cool the core and only gives about a 2C difference. The xp90C is probably better since it cools like the 120 and fits all mobos.

Tibors · Post by **Tibors** » Sat Apr 16, 2005 7:15 am

m0002a wrote:Has anyone actually considered trying it, rather than speculating about the theory?

Several people have. Just search the forums. I remember testing it with my XP-120, when I still had my Prescott chip. I can't remember the temp difference, which means it was either marginal (<2°C) or non existant.

One of the reasons theorising about this won't work is the effect of case airflow. You only know the results in your case if you test it, which was what I implied in the "third" point of my previous post.

P.S. Actually I can't find any theorising in the posts above the one I am reacting to now. In fact I pointed out that the reported differences where marginal.

Tibors · Post by **Tibors** » Sat Apr 16, 2005 7:26 am

mathias wrote:
Tibors wrote:One: When blowing down, the voltage regulators and the memory get additional cooling, which doesn't happen when blowing up.
Are you sure? They have to get at least some airflow from a fan pulling air away, plus a downward fan would be blowing air already heated by the CPU.

Take a fan. Let it blow towards your spread fingers and then let it blow away from your spread fingers. Feel the difference. I don't know the theory behind it, but airflow penetrates better between obstacles when a fan blows toward it than when it sucks away from it.

mathias · Post by **mathias** » Sat Apr 16, 2005 10:06 am

Tibors wrote: Take a fan. Let it blow towards your spread fingers and then let it blow away from your spread fingers. Feel the difference. I don't know the theory behind it, but airflow penetrates better between obstacles when a fan blows toward it than when it sucks away from it.

I think it's because blown air is forced in a certain direction, while sucked air comes from the path of least resistance. I don't doubt that blown air makes more contact with the components, but that is offset by the air being pre heated, and by an upwards fan usually bringing hot air pretty much directly to the case fan.

You can't simply test this, there are no temperature sensors on all those little things around the CPU.

Spod · Post by **Spod** » Sun Apr 17, 2005 7:02 am

FWIW, I had a problem with the RAM overheating on my system. Changing the fan from blowing up to blowing down improved stability. It's not especially scientific, but here's one voice with evidence that memory is cooled better with the HSF blowing down rather than up.

alleycat · Post by **alleycat** » Sun Apr 17, 2005 11:42 pm

I would have thought that having the fan blowing upwards is to allow for exhaust ducting, otherwise, what's the point? It's a great way to get heat out of the case so that other components can be kept cool. You can also get rid of a fan.