Dr Thermal TI-R8639L

Overclockers is supported by our readers. When you click a link to make a purchase, we may earn a commission. Learn More.

Light performance, low noise — Joe

SUMMARY: Not for aggressive P4 cooling, although relatively quiet.


Size: 88 x 86 x 59mm; Fan 33 cfm @ 3800 rpm.

Dr Thermal was nice enough to send a sample of their Dr Thermal TI-R8639L P4 heatsink. This is an aluminum radial fin design made by extrusion. The base


is flat and fully covers the P4 case; nothing extraordianry.

The fan is an T&T Model #MW-715H12C – a 70 x 15mm unit rated at 33 cfm @ 3800 rpm (this sample ran at 4050 rpm). I found it to be tolerably quiet – I measured its noise at 58 dBA with a Radio Shack sound meter 8″ from the fan’s intake, substantially less than a Delta 38 (about 69 dBA); Dr Thermal specs the noise at 34 dBA. It consumes about 5 watts, so it should be OK to use a motherboard fan header.

Mounting is its best feature – with the lever in the “up” position, engage the retention base; then swing the clip closed and it’s firmly mounted – easy, simple and very effective.

In summary, a fairly conventional aluminum extrusion heatsink with a very secure and easy to use clip.


The TI-R8639L was first tested on the CPU Die Simulator which gives results that are unaffected by motherboard influences. I then tested it on a Lucky Star P4A845D with a modified P4 1500 to read CPU case temps, as an example of what users might see on their systems.


Die Temp
Ambient Temp
54.6 C
23.0 C
31.6 C

TEST RESULTS – Motherboard

CPU Case Temp

Ambient Temp



MBM Temp

P4 1500, Lucky Star P4A845D

40.5 C

24.4 C



35 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.

Motherboard results place the TI-R8639L in the lower rank of heatsinks (Heatsink Ranking).


Not for aggressive P4 cooling, although relatively quiet.

Thanks again to Dr Thermal for sending this our way.

Email Joe


Leave a Reply