Thermal Paste Comparison, Part One: Applying Grease And More

Why Do We Test Each Paste In Four Scenarios?

In choosing four test platforms, I incorporate feedback from our valued readers. For instance, you wanted to see us take the cooler mounting pressure into account. We're skipping the LN2-based testing and focusing on scenarios you'll encounter in the real world. For example, we're using popular pre-assembled water coolers that should ensure heat sink temperatures below 60 °C (140 °F), premium aftermarket air coolers with back plates that should demonstrate high mounting pressure, and a run-of-the-mill budget cooler with push-pin mounting (that'll give us limited pressure). Stock coolers like that let the CPU get above 60 °C/140 °F (AMD) and 80 °C/176 °F (Intel).

Depending on viscosity and composition, not all pastes are a good fit for every application, nor are they all well-suited for novices. This warning also applies to replacing the heat sink on your GPU, and we'll discuss that separately below.

First, let's take a look at the three systems I used to test each thermal compound.

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Test System One: Closed-Loop Liquid Cooling
CoolerCorsair H80i
FanOriginal H80i fan, powered from an unregulated 7 V supply
MotherboardAsus 990FX Sabertooth
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Test System Two: Air Cooler with Back Plate (Screwed On)
Coolerbe quiet! Shadow Rock
FanOriginal Shadow Rock fan, speed set to 70%
CPUIntel Core 2 Quad Q6600 (Q0 Stepping) At 2.66 GHz
MotherboardGigabyte UP45-UD3LR
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Test System Three: Intel Boxed Cooler (Mounted with Push Pins)
CoolerIntel Boxed Cooler
FanOriginal Intel Fan, Speed set to 80%
CPUIntel Core 2 Duo E6850
MainboardGigabyte UP45-UD3LR

Testing Thermal Paste on a Graphics Card

This is a somewhat sensitive topic, and for safety reasons I excluded electrically conductive or liquid metal pastes from my testing. Since GPUs don’t have a heat spreader, but allow the cooler’s sink to directly sit on the die, I didn't want anyone to risk a short circuit.

I also used an older graphics card, which was convenient to test with. Its cooler was mounted using four screws and its fan speed could be dialed in to a constant value. Furthermore, I figured that an older card would be more tolerant of the higher temperatures I'd see. After all, we didn't want a cheap paste to destroy an expensive, current-gen board. Fortunately, the GPU die size and surface temperature are still comparable to modern mid-range cards.

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Test System Four: Graphics Card Test
CoolerZalman GPU cooler
FanOriginal Zalman fan, speed set to 80%
CPUAMD Radeon HD 4850
Test EnvironmentTest System 1 (see above)

Test Cycles, Test Duration and Settings

I should also explain how I took my measurements. Because the digital temperature sensors built-in to modern CPUs only give us uncalibrated Tcore values, I used the old way of measuring die temperature with a thermal diode under the heat spreader. The processors in this story still use soldered-on spreaders, so this value should be fairly accurate. I'll report the difference between Tcase and the room temperature, since that latter figure wasn't as constant as I would have liked through all of the benchmarking.

For the graphics card, I used the temperature as the GPU reported it. That number wasn't influenced by minor changes in room temperature.

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Test Environment
Room TemperatureApprox. 72 °F (between 70 and 73 °F)
Results of CPU TestsReported in °C as an average of temperature differences (Difference between the ambient temperature and the reading of the sensor under the heat spreader)
Results of GPU TestsReported in °C according to the temperature sensor on the GPU
Test Cycles CPU1 x four-hour burn-in, followed by break of at least two hours 4 x one-hour measurement, with one-hour breaks Total time at least 16 hours per thermal product and cooler
Test Cycles GPU1 x four-hour burn-in, followed by break of at least two hours 2 x one-hour measurement, with 30 minute breaks Total time at least 8.5 hours per thermal product
  • rolli59
    Nice article and bookmarked for reference. Looking forward for the next part.
  • alidan
    please tell me yo are also going to do the solder the heatsink to the cpu method? i forget what its called, but that is what i want to use for my next computer and would love to see how it stacks up.
  • The Von Matrices
    In the second section about advanced cooling methods, are you planning on discussing delidding CPUs and replacing thermal paste? If you do it might be worth mentioning that the delidding won't improve temperatures because of improved thermal paste conductivity but because of reducing the thickness of the paste. See
  • thasan1
    a really nice and helpful article!
  • stickmansam
    Huh, I do turn my heatsinks sometimes for optimal alignment so the heat pipes are perpendicular to the die. Depends if I got the room in the case and what ram is being used. Also heatsink dependent
  • slatts1024
    One of the best articles I've read on Tom's in years and that's saying something. Looking forward to part 2.
  • BigMack70
    ooooooooooh such a tease

    can't wait for part 2 - this was a great read!
  • Shankovich
    Loving that DHT-based design overlay picture on the first page. I've been telling my friends for a while to just get coolers with plated covers because the pipes miss the hotspot on intel CPU's, but no I'm full of bs apparently. This video is awesome btw, shows how spreads happen
  • nukemaster
    How many volts does this "7 volt" unregulated power supply put out?

    Just curious. I have some 8/9/12 volt regulators that would eliminate the guessing games for resistor fan adapters(voltage depends on the fans current draw).

    I have seen unregulated 6 volt power supplies range from 8-over 12 volts at low loads.

    For a rather low price you can use a regulator to get whatever voltage you want :)

    ohh yeah and...
    I can't wait for the next part of this to be release
  • jimmysmitty
    From what I have seen it depends on the materials. AS5 was great for a while but thee are better ones out than that now such as Noctuas or Zalmans.

    I also enjoyed using the IC Diamond thermal paste as it proved to cool very well but since it has a diamond based substance it can scuff the heat spreader.