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Asus custom coolers get caught in the CrossFire
The Radeon HD 4850 was an instant hit around these parts, but the first implementations caused us to raise (or is it singe?) an eyebrow over their thermals. Their single-slot coolers were never very beefy, and AMD tuned their fan speed control points pretty aggressively for good acoustics. The result was GPU temperatures approaching 90°C under load and idle temperatures around 80°C. Nothing to be worried about, according to AMD, but those temps were high enough to prompt us to look forward to 4850 cards with aftermarket cooling.

Asus' EAH4850 TOP looks to be just what we had in mind. This card has a custom-designed dual-slot cooler, and its GPU and memory clocks are tweaked up to 680MHz and 1050MHz, respectively, for a little extra performance. The EAH4850 TOP sells for $164.99 at Newegg right now, with $30 mail-in rebate (for those who enjoy the stimulating combination of paperwork and games of chance that is the MIR.) Like all Asus video cards, the EAH4850 TOP has a three-year warranty with no registration required.

Asus was nice enough to supply us with a pair of these cards for some CrossFire testing, and interestingly enough, we seem to have caught them in a board design transition. As you can see, the components are placed differently on the two cards. They have the same GPU and memory clock speeds, and should be functionally identical. For what it's worth, the card with the row of capacitors running across the back appears to be the newer layout, while the other one follows AMD's original reference design.

We should go ahead and address an issue we found with these cards up front, though. You'll see in our acoustic and temperature testing that the Asus 4850 was among the quietest and coolest cards we tested in a single-card configuration, with GPU temperatures under load that are quite dramatically reduced versus the stock Radeon HD 4850. But look closely at that cooler design, and you'll notice that it has a fan, not a blower, onboard. That little fan collects air from above itself and pushes that air down over the cooler's metal fins, an arrangement that's very effective in a single-card setup. But if you place another video card in the slot directly adjacent, as happens in CrossFire configurations on many motherboards, then Asus' cooler becomes starved for air, and GPU temperatures begin to climb.

We first noticed this problem during our performance testing, when our test system would lock up at random. There wasn't any particular pattern to it, except that we could run a game for while on it without issue, but eventually, inevitably, the screen would go black and the system would lock. Once we started troubleshooting with a eye toward a thermal issue, the problem became clear almost immediately. We didn't even have to make use of both GPUs. So long as a second card was nestled up against the Asus 4850, the Asus would overheat in a matter of minutes. You could watch it happening. Temperatures would rise, the card's fan speed would peak, and GPU temps would continue climbing. Eventually, within five to ten minutes, the temperature would climb past the 100°C mark, and shortly thereafter, the screen would go blank. Bam. Game over.

We tried everything we could looking for a fix. Swapping the two cards, which do after all have different PCB designs, was no help. Our Gigabyte EX58-UD5 motherboard has a rather large south bridge cooler that could obstruct airflow, so we tried testing on an Asus P5E3 Premium, as well—same problem. Asus even sent us a matched pair of EAH4850 TOP cards based on the new PCB design, but they showed the exact same behavior. In fact, I gave up on CrossFire altogether and mounted the EAH4850 TOP in the P5E3 Premium with a Radeon X1950 card adjacent to it, and the 4850 still overheated.

More alarmingly, all of this happened on our open-air test bench, where ambient temperatures are much lower than inside of the average PC.

We were in communication with Asus throughout this troubleshooting process, and at first, their R&D department said it couldn't duplicate the problem. After a little more testing, though, the company changed its tune. Asus now says it has made a revision to its card design, and it expects to be shipping the revised cards going forward. We hope to get our hands on one for testing soon.

In the meantime, you'll want to avoid buying this card, especially if you plan to run it in CrossFire or with a larger expansion card of any sort in the adjacent slot. There are plenty of other options. AMD's Radeon HD 4850 reference design may run a little hot, but at least it seems to be properly engineered.

Here's another Asus Radeon card with a gorgeous custom cooler, the EAH4870 DK 1G. "DK" stands for Dark Knight, and I was shocked to find a picture of a dude in black armor holding a lance on the front of the box. Where's Batman?

That disappointment aside, the 4870 DK is a nice example of a Radeon HD 4870 with 1GB of GDDR5 memory. You'll find it for $249.99 at Newegg, with a $20 mail-in rebate. No, it doesn't run at higher clock speeds than AMD's reference designs, but when we were gathering cards for use in this article, we had a very difficult time finding the combination of 1GB of RAM and "overclocked" speeds in a Radeon HD 4870.

Sadly, that sweet-looking custom cooler on the EAH4870 DK 1G has the same basic fan design as the Asus 4850. Like the 4850, the EAH4870's cooler is very effective in a single-card setup. In fact, it had by far the lowest GPU temperature we measured when used alone. But like the 4850, the EHA4870 suffocates when a card is placed in the slot next to it, blocking air to the cooling fan. The 4870 isn't as quick to heat up as the 4850, but the card still generates heat faster than the cooler is capable of removing it, so it's headed for the same destination.

Moving to different a motherboard than our EX58-UD5 helped somewhat by slowing down the rate at which the card overheats. Still, we saw the EAH4870's MEMIO sensor reach GPU temperatures in excess of 116°C in testing on the Asus P5E3 Premium, and getting there only took about 30 minutes of continuous GPU use. We found we could almost reverse the equation by using Asus' SmartDoctor utility to set the fan speed manually at 100%—but doing so was dreadfully loud, as the fan reached a speed it apparently won't hit when relying on the card's automatic speed control.

The bottom line is that this cooler is unsuitable for use in any situation where a second card obstructs its fan from taking in air. We don't yet have word from Asus how it plans to address this problem with this product, either. Again, I'd advise you to seek out an alternative 4870 card. In this case, AMD's stock cooler is really quite good.

If you've purchased either of these cards and are experiencing system lock-ups or heat-related GPU problems, I'd suggest contacting Asus for a warranty replacement immediately. They should take good care of you. If they give you any trouble about it, feel free to drop us a line at I'm not sure we can do anything to help, but we'd like to know if these issues aren't being addressed properly.

The problems we encountered with these cards aren't endemic to just Asus, either. Sapphire's 4850 X2 cooler is a bit clumsy and loud, to name just one other example. A number of board vendors have latched on to the idea of offering their own coolers, and they seem to target two things: the cooler must be a custom design, and it must use multiple slots. Those things alone aren't necessarily good, though. I'm perplexed why anyone would offer a dual-slot cooler that isn't expressly designed to direct hot air out the back of the PC. But many do.

AMD and Nvidia clearly invest considerable engineering effort in their stock coolers, to make sure they have good acoustics and tolerate a wide range of conditions. Look at the way the blower on the GTX 285 card is angled slightly; that's so it can take in air even if another card is right next to it. If a board vendor doesn't intend to invest sufficient engineering effort into building an even better cooler than the stock one, then why bother?