SPCR's 2010 CPU Heatsink Test Platform [Updates: 10 April & 31 May]

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POSTSCRIPT: O THE TESTING LIFE!
April 10, 2010
by Lawrence Lee & Mike Chin

Two months after this article was published, while using the i7 test platform after a several weeks hiatus to test a new pair of heatsinks, we noticed that the temperature readings had changed... and perhaps become unstable. The heatsinks in hand were the Cogage TrueSpirit, a cut-down version of the Thermalright Ultra-120, and the Zalman CNPS10X Quiet, which has wider fin spacing than the CNPS10X Flex and Extreme variants. The Ultra-120 and CNPS10X Extreme had finished in 6~7th position on our chart in February (when cooled with the reference 120mm fan), so we were stunned to see the TrueSpirit and CNPS10X Quiet both performing at levels rivaling the Prolimatech Megahalems and Noctua NH-D14, the current champions. The tests were repeated twice, with the same results.

This called for a complete retest of several reference heatsinks, at the end of which we were dismayed to discover that the core temperature in the test platform had dropped significantly, basically overnight, and every heatsink was suddenly producing cooler CPU temperatures. In addition, we noticed that both temperature and power consumption was swinging high/low at random intervals after a period of CPU stress operation, but only when the system was overclocked/overvolted.

After much more experimentation, we learned that the same behavior was evident with different processors, so we suspected the board had been damaged, perhaps by the 1.4V overvolt applied in our stress testing. In the end, we had no choice but to replace the board. We asked Asus for a new motherboard with better power regulation, and in response, they sent us the current top-of-the-line LGA1366 board, the P6X58D, which uses a 16+2 phase power design.


Asus sent us one of their new top-of-the-line P6X58D Premium to be our replacement i7 heatsinks test platform. It has the benefit of a sophisticated 16 + 2 phase voltage regulation module design.

After some testing on the new board, we found that the problem persisted, though it did take longer for the temperature and power to begin fluctuating. Dialing back the CPU voltage helped somewhat. After a few more days of systematic testing, we decided the system should be run at stock settings from now on, to avoid any potential inconsistentcies in the power/thermal load. We would prefer to have the processor run as hot as possible, but it is more important that we can obtain stable results over a lengthy period of time, due to the method in which we conduct our heatsink testing (typically with both the stock and reference fans at various speeds).

i7-965 Platform Power Consumption at Load
(w/ Prolimatech Megahalems heatsink & reference 12cm fan @1000 rpm)
Motherboard
(RAM configuration)
Setting
System (AC)
System (DC)
Thermal Rise
P6T SE
(single channel)
Stock
168W
148W
35°C
3.6 GHz, 1.4V
215W
194W
50°C
P6X58D Premium
(triple channel)
Stock
199W
179W
38°C

One of our readers had noted that we were testing using only a single channel memory configuration and that more memory would increase power draw, so we switched to triple channel RAM. This change had an enormous effect on power consumption, bumping it up by more than 30W at the AC outplet. Oddly, however, the increase CPU temperature was virtually nil. There was also little increase in the current at the AUX12V socket, which suggests that the memory controller was responsible for much of the power increase, on the 5V and 3.3V lines.

In any case, the change in motherboard and test platform settings meant a complete retest of all the heatsinks we've tested on the i7 platform thus far. This was a tedious, repetitive task that took two days, even though only the Nexus 120 fan was used.

Heatsink Re-test Results

Original i7 Test Results: °C rise Comparison (Stock Settings)
Heatsink
Nexus 120mm fan voltage /
SPL @1m
Rank
12V
9V
7V
16 dBA
13 dBA
12 dBA
Noctua NH-D14
36
38
41
#1
Prolimatech Megahalems
35
39
42
#1
Scythe Mugen-2
37
40
43
#3
Noctua NH-U12P
38
40
41
#3
Thermalright U120 eXtreme
38
41
45
#5
Zalman CNPS10X Extreme
39
43
48
#6
Thermalright U120
42
44
49
#7
Zalman CNPS10X Flex
42
45
49
#7
Scythe Kabuto
43
48
54
#9
Noctua NH-C12P
44
47
54
#9

There were only a few changes in rank. The CNPS10X Extreme slipped from #6 to #8 due to an average 4°C increase in thermal rise. The downblowing Kabuto fared 6°C worse, remaining in last place but this time alone as the NH-C12P held its ground and actually improved two ranks because the Zalman CNPS10X Extreme and Flex slipped slightly. At the top of the spectrum, little changed with the Megahalems and NH-D14 battling for top position, though this time joined by the smaller NH-U12P.

New i7 Test Results: °C rise Comparison
Heatsink
Nexus 120mm fan voltage /
SPL @1m
12V
9V
7V
Rank
16 dBA
13 dBA
12 dBA
Prolimatech Megahalems
38
41
44
#1
Noctua NH-D14
38
42
45
#2
Noctua NH-U12P
39
42
44
#2
Scythe Mugen-2
39
42
45
#4
Thermalright U120 eXtreme
40
43
48
#5
Thermalright U120
42
45
49
#6
Noctua NH-C12P
43
47
51
#7
Zalman CNPS10X Extreme
43
47
53
#8
Zalman CNPS10X Flex
45
50
54
#9
Scythe Kabuto
51
53
60
#10

The new results are indicative of at least one significant aspect of heatsink testing: It seems almost impossible to get exactly the same results from one set of tests to the next (even when the same CPU and motherboard are used). There are a couple of possible reasons:

  • The thermal measurement tools simply don't have fine enough resolution; perhaps the accuracy of the digital termistor in the CPU is worse than +,-1°C.
  • It may be impossible to apply the same amount of TIM and get exactly the same degree of tension on the heatsink during mounting, the end result being variations in results from different instances of testing the same heatsink on the same platform.

For now, the new i7 test results table directly above will remain the reference point for comparing against future heatsink tests. We move on.

* * *

FLASH! See 31 May 2010 Postscript on Test Platform for Smaller Heatsinks, overleaf.

Discuss this article in the SPCR forums.



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