Thermalright SLK-900-U

Outstanding performance, depending on fan used – Joe

SUMMARY: An excellent choice for aggressive CPU cooling, but noise may be an issue.


The good guys at Thermalright were nice enough to send their latest, the SLK-900-U for a test spin. This is the largest of the SLK series – it measures 99mm x 55mm x 43mm high – without fan – and weighs in at about 570 grams. Due to its size, only 80mm and 70mm fans can be installed if used for P4 cooling with the standard retention bracket.

The SLK-900-U ships with parts for Socket A and P4 mounting:


For P4 use, users have the option of either using the standard retention bracket or removing the bracket and mounting it with spring-loaded bolts; this option requires removing the motherboard form the case. For AMD use, users must remove the motherboard – the SLK-900-U uses the backing plate and spring-loaded bolts. I have not tested it on a motherboard yet but will shortly.

In addition, fans ranging from 70 to 92mm can be mounted on the SLK-900-U, with the exception noted above.

The base is well finished:


When I ran my nail over it, I could not feel or hear any ridges.


I tested the SLK-900-U with Vantec’s Tornado, a Sunon 80 x 38mm fan, model #PMD1208PMB1-A rated at 84.1 cfm @ 5700 RPM, 55.2 dBA, 9.1w; this fan features vanes in the base to straighten airflow off the blades. I also used a 92mm fan, an ADDA model #AD0912UB-A71GL, rated at 60 cfm @ 3300 rpm, 39.4 dBA 4.7w. I varied voltages to get a range of fan speeds and measured rpms using an Omega digital tachometer.

I measured fan noise with a Radio Shack sound meter 8″ from the fan’s intake. These are not comparable to noise levels reported by fan manufacturers; noise is usually measured at three feet from the fan.

The SLK-900-U was tested on the CPU Die Simulator which gives results that are unaffected by motherboard influences.


Die Temp
Ambient Temp
SLK-900-U, Vantec 80, 5530 rpm, 74 dBA
39.2 C
24.0 C
15.2 C
SLK-900-U, Vantec 80, 3995 rpm, 66 dBA
41.1 C
23.6 C
17.5 C
SLK-900-U, Vantec 80, 3000 rpm, 56 dBA
43.9 C
24.3 C
19.6 C
SLK-900-U, AADA 92, 3934 rpm, 65 dBA
42.2 C
23.8 C
18.4 C
SLK-900-U, AADA 92, 3244 rpm, 56 dBA
45.5 C
24.8 C
20.7 C

Delta = CPU temp – Ambient Temp
C/W = Delta / CPU Watts

Interpreting C/W: For every watt (CPUw) that the CPU
consumes, the HSF will limit the CPU’s temperature rise to (C/W x CPUw)
plus the temperature at the HSF’s fan inlet. For example, at an ambient temp of 25 C, a C/W of 0.25 with a CPU radiating 50 watts means that CPU temp will increase 50 x 0.25 = 12.5 C over ambient temp, or 37.5 C. The lower the C/W, the better.

Die Simulator results place the SLK-900-U in the top rank of heatsinks tested to date (Heatsink Ranking). Note that at about the same rpms, there is no major difference between the 80 and 92mm fans.


Thermalright’s SLK-900-U is an excellent choice for aggressive CPU cooling. However, the more aggressive the fan used, the higher the noise level – no surprise. At a minimum, a rheostat might be required if your PC is “24-7”.

Thanks again to Thermalright for sending this our way.

The SLK-900-U will be available from The Heatsink Factory.

Email Joe