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.

Test System One: Closed-Loop Liquid Cooling
Corsair H80i
Original H80i fan, powered from an unregulated 7 V supply
AMD FX-8350
Asus 990FX Sabertooth
Test System Two: Air Cooler with Back Plate (Screwed On)
be quiet! Shadow Rock
Original Shadow Rock fan, speed set to 70% 
Intel Core 2 Quad Q6600 (Q0 Stepping) At 2.66 GHz
Gigabyte UP45-UD3LR
Test System Three: Intel Boxed Cooler (Mounted with Push Pins)
Intel Boxed Cooler
Original Intel Fan, Speed set to 80%
Intel Core 2 Duo E6850
Gigabyte 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.

Test System Four: Graphics Card Test
Zalman GPU cooler
Original Zalman fan, speed set to 80%
AMD Radeon HD 4850
Test Environment
Test 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.

Test Environment
Room Temperature
Approx. 72 °F (between 70 and 73 °F)
Results of CPU Tests
Reported 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 Tests
Reported in °C according to the temperature sensor on the GPU
Test Cycles CPU
1 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 GPU
1 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
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    Your comment
  • 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.
  • stickmansam
    Also would like to see an Ivy/Haswell test system since they run pretty hot and imo, they need more study on how to best cool them due to the TIM inside them.
  • rmpumper
    I always spread the paste manually. Never had issues with overheating.
  • smeezekitty
    I am using dirt cheap masscool fanner-420.

    My temps are quite good - really the choice of cooler is much much more important than the choice of paste.
  • SteelCity1981
    "don’t apply too much. Otherwise, the paste will ooze out on all sides. If your paste is electrically conductive, you can almost be assured of hardware damage."

    Tell this to OEM's ever seen a hp, dell, Lenovo, Asus, Acer cpu after you take off the heatsink with thermal paste on it? it's oozed all over he place...
  • JimmiG
    I experimented with different application methods when I built my 4770K-based system. Small dot, large dot, X, line. No real difference, but the small dot produced the best results by ~2C. I used MX-4, which is so easy to apply that you can't really mess up.

    When delidding and applying Liquid Pro between the IHS and die, I "painted" a very thin layer. It was very difficult until the surface tension broke, then it was easy from there.
  • giovanni86
    Nice article, you guys ripped me a new one with the spread all over cpu method. Been doing that for a long time hah. Based off what you guys said i feel like it need to reapply paste considering the hot spot on my ivy bridge processor. I feel as if that method works although its very tedious and takes a long time to apply a even surface, i used Arctic MX-2 and it seemed to apply easy with some resistance to spreading evenly flat.. 30 minutes later walaa.. haha painted flat all over.. But i like that pea method in the middle seems to cover the hot spot quite well. Will have to try that out. Can't wait for the next part.
  • urimiel
    Dude! this is great. This the first time since the Coppermine era that we started using thermal pastes widely that somebody put all the information together. Congrats guys great job. Well done.
  • zyky
    2.66Ghz Q0 Q6600? What planet did I stumble upon? Hopefully one that still has Indigo Xtreme.
  • James Hood
    Hey Tom's, I realize that you guys have limited time for these articles, and have to limit the scope. But I think it should be pointed out that not every one reading these articles are complete novices. In fact, I would wager those of us wanting to see the subtle differences between paste and cooler combinations are intermediate to advanced users. As such, in the future I think the risks involved should be left up to the reader. Having the comparison data to go with the risk would be helpful. Gaining .5C better temps for me would not be worth it. But if it dropped 2C on a GPU for my laptop... now that is tempting. As it stands, this data will not be available for those of us that would be interested.

    Otherwise, great article, can't wait to see the results.
  • 4Ryan6
    Nice Job Igor, You have your ambient controlled for the tests and very good illustrations of contact imperfections and CPU hot spot area!

    I know you're glad to be nearing the end as that was a lot of time invested to completion.

    Congratulations sir, on one of the best reviews I've seen come from Toms yet!

  • edlight
    Direct touch heat pipe heatsinks do not have air between the pipes where they contact the cpu. There's the block that they are set into. No mention was made of lapping heatsinks. 16 and 8 hour breakins for paste is way too little, so the fast breaking in paste will have an advantage.
  • Tass1234
    Hi, i would love to see tests done with a couple of the best pastes comparing the amount of cooling between the paste been applied spread with a credit card or similar and applied by the pressure done by the sink. Would be much better than just saying spreading is bad because you can create air bubbles because we can't compare by the sayings here what is better, if spread by pressure or spread by hand if is done well and without bubbles (and of course with an easy to spread paste like MX4). Thanks :D
  • m32
    I've bee trolled!!!! lol. I'm looking forward to part 2. This is an great read for us hardware geeks.
  • besterino
    IMHO Igor's articles are the best (any maybe not only on Tom's). Always a worthy read, sometimes even a funny one. :D And dammit, he's versatile (not only the nomral stuff, but also keyboards, speakers, you name it, he's got it covered - in detail.)

    Yeah, I'm a fanboi.