Case ReviewsComparisonsCooler Master

Cooler Master Pi CASE 40 for Raspberry Pi 4 (GPIO WARNING!)

Update 21 October 2021: Cooler Master have released a revised version of this case without, the Pi-Case-40-v2. This addresses the issue with the mirrored GPIO pins. I’ve no intention of purchasing this case to test the new version, but I’m pleased that it now exists. The issues with their pi-tool software still remain unresolved, so best still to avoid using that.

If you’ve read any of my other Raspberry Pi 4 case reviews, you’ll know I’m a fan of passively cooled cases. Learning that Cooler Master was entering the Raspberry Pi case market was an interesting development. Pitched originally on Kickstarter, the Cooler Master Pi CASE 40 is described as “The travel case of Pi enthusiasts, by Pi enthusiasts”, I was optimistic they would build on the experience of the community to create something special. Afterall Cooler Master has been making PC case, cooling products and other accessories, so have the design experience, skills and budget beyond the more typical specialist Pi Case makers.

The aluminium shell mates with the Raspberry Pi processor to transfer heat and keep the Raspberry Pi 4 running cool. The “travel” aspect of this case design, seems to be about combining aluminium with a softer rubber/TPU bumper around the case. I’ve mixed feelings about the TPU bumper, but more on that later.

My testing has shown that this case shows promise, but it’s let down firstly by a fundamental design issue and secondly by the software made available with the case.


The Cooler Master Pi CASE 40 arrived in a neat cardboard box, with clear assembly instructions printed on the inside surfaces of the box, avoiding the need for an extra printed instruction booklet, clearly, some thought was given to minimising waste. Under a lift up section is printed a QR code which takes you to the Cooler Master Pi CASE 40 product page, where you’ll also find the download instructions for the software along with some accessories which can be 3D printed. Inside the box, you’ll find the case, along with 4 bolts and an Allen key to secure the case together, 2 thermal pads (nice to see a spare included) and 4 plastic wings which can be added to the case so that it can be attached using the standard VESA mounting system (75×75 or 100×100). The instructions also suggest you could use a couple of the mounts to wall mount the case. I’ve tested any of the mounting options.

Turning to the Cooler Master Pi CASE 40 itself, the aluminium shell covers the top and partly down the sides, the bottom of the case is made of smoked plastic, which still allows the power and activity LEDs to be easily seen. An outline of the hexagonal Cooler Master logo is featured on the top and bottom of the case, as a mirrored metal element on top and imprinted into the centre of the plastic case. The plastic base also features two rubber stips, which hint at some of the hexagonal shape of the logo. I have to admit the “feet” on this case are the best I’ve experienced. So many other cases use flimsy stick on circular feet that seem to easily come off, especially when the case gets warm. The strips on the Cooler Master Pi CASE 40 are securely fitted from the factory and haven’t shown any signs of movement.

The TPU bumper wraps the sides of the case, along with covering a small section of the top. It has a slot on the end to allow thin ribbon cables to be fed out for a camera or display. It has flaps that cover the SD-Card slot and the GPIO connections which are present on the side of the case, instead of the top, this has some issues which I’ll cover later. This flap covering the GPIO is quite stiff and a little awkward to use. The bumper on the top of the case is where you’ll also find the “re-mappable power button”. The TPU bumper is attached fairly securely to the case though 14 moulded mounting points that protrude out and interface at the joints between the aluminium and plastic sections of the case. I did find the bumper didn’t sit right around the USB ports, bowing out slightly (which you might be able to see in the image above), but I doubt many other people would notice.

Cooling Design

I’ll come on to cooling performance test results shortly, focusing on the design first. The aluminium top case shell has a raised section to mate with the Pi processor, similar to that used in larger Argon ONE, though with extra ridges that run on the inside of the case and further increase the surface area and help with heat dissipation. Unlike the Argon NEO, it doesn’t heatsink the memory chip, which is reasonable, as I’ve not seen any issue with memory temperature being a problem, even in overclocked tests. It’s unclear if having a TPU bumper around portions of the case will hamper heat dissipation.

Weighing the case and some competitors, firstly fully setup including a Raspberry Pi installed, then with all just the metal components of the case. For the Argon NEO, this meant removing the Pi and the plastic base, for the FLRIC I removed the Pi and the plastic base and popped off the top plastic top cover, for the Pi CASE 40 I removed the Pi, the plastic base the TPU bumper and removed the board which relocated the GPIO and adds the power button.

CaseWeight (g)Metal Weight (g)
Argon NEO14580 (40 excluding top lid)
Cooler Master Pi CASE 4018580

With the three cases fully dismantled and weighed, some surprises are revealed. The FLIRC case which has the top and sides made from aluminium actually contains the least amount of metal. Probably in large part to the design using a hollow section to interface to the processor, rather than a solid block. The Argon NEO weighs in the same as the Cooler Master Pi CASE 40, that is until you remove the top lid, when it then loses 50% of its weight. Given the lid section is only attached to the base plate via magnets, the thermal transfer won’t be as good as the one-piece design of the Cooler Master Pi CASE 40 aluminium top section.

With the total mass and heat sink design, the Cooler Master Pi CASE 40 should do well in the thermal testing.

GPIO Access

Maintaining access to GPIO pins is a challenge for all case designs, with several cases not providing access at all. The Argon NEO accomplished this with a two-piece top shell design. The Cooler Master Pi CASE 40 opted to relocate the GPIO header to the side of the case behind the stiff TPU flap, however in doing so have made a fundamental design error.

To present the GPIO pins on the side of the case, there is a daughterboard that connects to the Raspberry Pi when it’s installed in the case. The board in my case is labelled “C2146-01-SJ”, this includes a surface mount 40 pin socket on one side and a right angle 40 pin through-hole header (along with the power button) on the other. For reasons I can’t understand, and can only put down to the incompetence of the designer, the board results in mirroring the pin rows of the standard Raspberry Pi GPIO header. This makes it all too easy for someone to mistakenly wire connections to wrong pins, some with likely fatal (to the attached component) consequences. For example, the 5V and 3.3V pins are swapped positions!

If you read the website carefully you’ll find the following note:

“NOTE: Side access to the GPIO only allows the use of jumper cables. Pi Case 40 is not compatible with devices that only require direct connection to part or the entire GPIO of the Raspberry Pi with traditional layout. Please see the product images for more information on the GPIO pin layout on the Pi Case 40.”

Cooler Master – Pi CASE 40 Product Page (6 March 2020)

This “Note” should be a clear warning. Not only does it make it incompatible with any Pi HAT, but it’s likely people won’t notice until it’s too late and they’ve caused damage.

The case does feature a pinout label, however unlike the clear white on grey text printed directly on the case shown in the Kickstarter prototype images (and used on the Argon NEO), instead there is a clear label with black text stuck on to the side of the case. This black on grey is hard to read, hindered further by the reflective clear tape it’s printed on. The label isn’t applied straight and level on my case, nor on the case used for product images on the Cooler Master website. The text in the image below is a lot clearer due to the lighting than it is normally.

I think Cooler Master should quickly look to replace the daughterboard with a fixed design that doesn’t mirror the pins. I honestly can’t understand how a product pitched as “The travel case of Pi enthusiasts, by Pi enthusiasts”, could have been released with this flaw. There is nothing about the PCB design limitations that should have caused this.

Update 7 March 2021: Thanks to Reddit user /u/farptr for pointing out that the community did raise the issue with the GPIO header during the crowdfunding phase, but Cooler Master opted not to fix it. Instead, the community have stepped with a new header you can get manufactured: but this really should be necessary.

Re-Mappable Power Button

The Cooler Master Pi CASE 40 “includes a button that shortens pin 5 and 6 when pressed (GPIO3 and GND)”, the wording could be improved, such as the button pulls pin 5 (GPIO3) low when pressed. GPIO3 is used to enable the “Wake from Halt” capability, which enables the button to be pressed to boot a pi that has been halted, rather than needing to cycle the power to the Pi. Unlike the Argon ONE power switch, the Pi in the Cooler Master Pi CASE 40 will power on immediately when power is applied.

Using the Pi-Tool software the button can be configured to perform different actions in response to a series or long or short presses, I’m sure some will find this useful.

Cooler Master Pi Tool Software

Linked from the Cooler Master Pi CASE 40 product page are instructions on how to install “Pi Tool” which offers a UI to apply some overclocking profiles which have been validated by Cooler Master for use in this enclosure. The tool also offers the capability to assign functions to the button actions, from anything as simple as a long press triggering the Pi to shutdown to sequences of presses launching other applications. The final part of the tool is to provide monitoring of system metrics, where it plots graphs for core temperature, core frequency, memory usage and system load average. There are issues with this monitoring capability I’ll come on to shortly.

At time of writing the overclocking profiles are:


The top end profile isn’t as a high as some previous overclocks I’ve run, but provide noticeable improvements in the Performance of the Pi.

Installing Pi Tool

To install the Pi Tool Software, you need to copy and paste a series of commands from the product page, which downloads a shell script from GitHub and executes it:

curl -o
chmod +x

You can see the shell script here. At time of writing this is what the script does:

  • Downloads the latest release of the pi-tool.deb package (68.1MB) along with a desktop wallpaper image cm_wallpaper.jpg (3840 x 2160 – 4.95MB)
  • Asks the user if they wish to install “Cooler Master desktop customizations”?
  • If YES:
    • Apply the previously downloaded wallpaper image
    • Clones from GitHub (480MB)
    • Modifies some of the CSS to adjust some of the colours in the theme and copes the theme to /home/$USER/.themes/Adapta-CoolerMaster
    • Offers to apply the theme now, or explains to use lxappearance later to apply the theme.
    • The script continues with Pi Tool installation
  • Installs the pi-tool.deb package

Starting with a clean Raspberry Pi OS with desktop dated Jan 11th 2021 and fully updated with all updates as of 24th Feb 2021, installing just the pi-tool package (0.3.1) requires 22 additional packages, 355MB. This seems quite heavy for a small utility.

The package offers two binaries, /opt/Cooler Master Pi Tool/pi-tool and /opt/Cooler Master Pi Tool/bin/pi-tool-daemon the latter of which I believe is for handling the actions of the power button.

Running Pi Tool

The utility can be run by starting it from a terminal with the command pi-tool or navigating the Menu: Accessories -> Cooler Master Pi Tool. Note that clicking the “x” to close the utility, just minimises it to the panel in the top right of the screen, you need to right-click on the icon and select “Quit”.

As described previously the Pi-Tool provides a simple UI for system monitoring, and also applying overclocking profiles. There is a couple of significant problems with this software. As you can see from the image below, as soon as Pi Tool is started, the system load increases rapidly from ~0.1 to ~2.0 and temperatures start to rise. You’ll also see that despite nothing else running, the core frequency is running at full speed, it’s not dropping back to the 600MHz idle clock speed you’d expect. This is because the pi-tool is busy burning CPU cycles collecting and graphing the data, roughly using the equivalent of between 1 and 2 cores. Closing the tool to the docked area still has it using 4-15% CPU.

Resource utilisation at this level is unacceptable for a monitoring tool. I’ve raised a couple of issues against the GitHub Repo:

Until these issues are resolved I can’t recommend using the Pi Tool software. If you wish to overclock, just use add the parameters in the /boot/config.txt file instead of using the tool.

Thermal Testing

To test how the Cooler Master Pi CASE 40 compared would perform relative to the competition, the new enclosure was tested concurrently with previously tested cases, the Argon NEO and the FLIRC. Note during the different rounds of testing the ambient temperature did vary significantly, as such comparing between test scenarios is not possible.

  • Image:
  • Updates: All updates as of 24 February 2021
  • Kernel: Linux raspberrypi 5.10.11-v7l+ #1399 SMP
  • Firmware:
    • Bootloader: Thu 3 Sep 12:11:43 UTC 2020 (1599135103)
    • VL805 USB 3.0 Firmware: 000138a1
  • Software/Configuration:
    • WiFi disabled
    • SSH enabled
    • Samba installed and configured
    • Stress
    • Stressberry
    • Python 3.7.3
  • Load test configuration
    • Stress active concurrently on all 4 cores
    • 5 minute idle period (once the temperature has reached a steady state)
    • 30 minute stress test.

Stress Test Results: Console

Testing with system booted to the terminal, no GUI running.

None of the cases hit thermal throttling limits, the Cooler Master Pi CASE 40 has a clear performance advantage over the competition. Removing the top lid on the Argon NEO closes the gap a little.

Stress Test Results: Desktop GUI (Pi Tool Impact)

Testing with system booted to Desktop GUI with Cooler Master Pi CASE 40 running Pi Tool software

Running the Pi Tool utility causes the base start temperature of the Cooler Master Pi CASE 40 to be considerably higher as the utility effectively places a partial stress load on the system. Once all 4 cores are fully loaded the gap to the competition still remains.

Stress Test Results: Console Overclocked

Testing with the system booted to a terminal prompt, no GUI running. The systems were all overclocked with the following settings, equivalent to the +30% overclock profile in the Cooler Master Pi Tool.


With all the systems overclocked, the Argon NEO and FLIRC cases both hit the thermal throttle as they approach 25 minutes of full 4 core stress with very similar temperatures. The Cooler Master Pi CASE 40 continues to lead the pack in the tests, never throttling and ending the test around 10°C away from the thermal throttling threshold. The TPU bumper doesn’t stop it from outperforming all the other cases in this test.

All the cases get hot to the touch during the stress as they passively radiate the heat into the surroundings.

CaseIdle Temperature (°C)Stress Temperature (°C)
Argon NEO3351
Cooler Master Pi CASE 403453
External Enclosure Temperatures During Thermal Testing


The Cooler Master Pi CASE 40 delivers best in class passive thermal cooling, keeping your Pi away from thermal throttling limits when running stock or overclocked. However, this comes at a price, in the UK this case was £24.99 from Amazon, compared to the Argon NEO £17 and the FLIRC cases £16 + shipping from The Pi Hut. However, if you really want to overclock your Pi and keep it fanless, then this might be the case for you.

The TPU bumper makes accessing the GPIO ports more difficult, and reading the poorly printed label even more difficult, but doesn’t appear to impact thermals. The large feet keep the case secure on any surface and don’t show signs of being able to easily fall off like so many other cases.

As mentioned above, I suggest you stay away from the Pi Tool software, it not fit for purpose, at least at the moment.

Finally, the biggest issue I have with the case is the reversed GPIO pinout. I know this is sort of mentioned on the Cooler Master product page and several other online reviews have mentioned it. However, I think this is a dangerous flaw that is likely to impact anyone who doesn’t pay very close attention. It might also cost you extra money if you send 5V to a 3.3V component/sensor you attached inadvertently to the wrong pin on this Pi case.

Improvements I’d like to see from Cooler Master:

  • Replace the GPIO daughterboard with one that doesn’t reverse the pins – Don’t let customers make mistakes or feel they need to get a replacement manufactured using a community design.
  • Print the Pinout on the case in white text, like in the Kickstarter prototype images. Don’t use a cheap stick-on label.
  • Make the TPU flap that covers the GPIO more flexible so it hinges out more easily, or reconsider the design of the GPIO area altogether.
  • Fix the software, a monitoring tool shouldn’t apply significant load to the system.

Product Links

Amazon links are affiliate links which help support the site, where possible I’ve used links which should take you to the product in the Amazon store in your region. Links to other suppliers are included for your convenience.

6 thoughts on “Cooler Master Pi CASE 40 for Raspberry Pi 4 (GPIO WARNING!)

  • Could you please run a WiFi test? Also, how does it compare to the passively cooled Armour?

    • Hi Tom, I pretty much concluded in my last attempt at WiFi testing, that attempting to quantify WiFi performance in a home environment has too many variables which can’t be controlled, making precise results impossible. So until I can come up with a more reliable test method (if even possible), I’m a little reluctant to do further WiFi tests.

      Suffice to say I’m currently using the Cooler Master case, with WiFi for my Home Assistant server and WiFi hasn’t been a problem. Though I’m about to swap this for an Argon ONE M.2 case now the WiFi issues have been resolved on that case.

  • Thank you so much for detailed review. I knew the pinout was different for the case but I didn’t know that it was not compatible with the HATS. I was almost going to give it a try for the UPS HAT.

    • As mentioned in the update to the post the pinout of the GPIO has been corrected on the latest version. This means you could now attach a HAT, though it would end up being perpendicular to the case, so look a bit odd. It also won’t be suitable for any HAT that uses the 4 PoE pins on the mainboard of the Pi.

      As there are several alternatives to the Coolermaster case without the compromises it brings, I suggest going with something else.

      • Thanks for the reply!

        I checked carefully and noticed that my version is the “wonky GPIO pins” one!

        But didn’t want to leave my good cooler case and decided to check out necessery GPIO pins from the Waveshare website in order to use my UPS HAT.

        I use this picture to connect Cooler Master’s GPIO pins to the UPS HAT’s GPIO pins.
        ( )

        Even without the HDDs attached, RPi 4 booted with a “Low Power” warning.

        So I thought the pin cables I used were not carrying enough power between UPS HAT and the Pi.

        I turn off the UPS HAT and used a usb type-c cable to feed the Pi 4’s type-c port.

        If I’m not mistaken, now UPS HAT powering up my Pi 4 via usb output and I can check the battery percentages and stuff via pinouts.

        I booted up my Pi when HDDs attached and it worked without any power warnings.

        Sorry for the long comment. Thank you so much for inspiring me!

        • OK, an update:

          I unscrewed that stupid reverse 90 degree GPIO pins from cooler master case and replace it with a normal 90 degree GPIO pins. I lost the ability of a case button but I wasn’t using it anyway.

          Now I can attach my UPS HAT easily and I have the benefit of cooler master case’s giant heatsink.


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