Modding the ASUS RT-AX88U with a cooling fan

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Asus RT-AX88U

I recently got myself an ASUS RT-AX88U router as an upgrade from my existing ASUS RT-AC87U. The ASUS RT-AX88U has a relatively large footprint. Its casing has a large open vent and most of its bottom side is vented to allow heat from the quad core processor to dissipate passively.

The bottom of the ASUS RT-AX88U​
The bottom of the ASUS RT-AX88U

What I like best with ASUS’ routers is the ability to update it with a 3rd party firmware, the most popular being the the Asuswrt-merlin firmware. Amongst the many configurations and tools, one that I typically check is the router’s internal temperatures as you can see from the screenshot below. As you can see, the ASUS RT-AX88U‘s CPU averages at around 79°C-80°C (174°F-176°F) while both the 2.4GHz and 5GHz Wifi modules averages around 50°C-51°C (122°F-124°F) with an ambient temperature that averages around 30°C here in sunny Singapore.

asuswrt merlin firmware temperature check

As 80°C does seems rather hot, I wondering if modding the ASUS RT-AX88U with a cooling fan and and bring the temperatures down make any difference?

Modding the ASUS RT-AX88U with a cooling fan

I happened to have a low profile 70mm fan lying around from a very old CPU heatsink that is no longer used. When I tried to place it on top of the ASUS RT-AX88U router, it looks to fit rather perfectly over the top vents as you can see from the results I got below. The solution to keep the fan in place is a simple one. Just use a simple blue tack. And since it’s flexible, it would also absorb any vibrations from the fan.

The only problem is to power the fan as it uses the regular 3-pin connector that are common with CPU cooling fans. But even so, this isn’t really a major blocker as the ASUS RT-AX88U router provides 2 USB 3.0 ports, one in the front and another at the back. I’ve already use the back USB port to power my RaspberryPi which I use to run Homebridge to enable Apple Home and Siri support to manage my non-Homekit supported devices. You can find out more about this little project here on this post.

Modding the cooling fan with a USB connector

For a small 70mm cooling fan, the 5V DC power supplied from the USB port would be more than enough to spin the fan. If you are experienced and handy with electronics, this is a simple matter of just striping out some wires and soldering together some cables. Of course, you will need to sacrifice an existing USB cable. But I would think that this should not be a problem since almost every device these days provides one. I myself have many of those micro USB cables for my various devices that’s just lying around.

Striping out the wires and soldering them together

As you can see, above, all you need is to join the black and red cables together and leave the rest disconnected since all you want is the 5V power supply. If you have heat shrink tubings, I would recommend that you use those to properly wrap up the exposed parts of the cable after you’ve soldered them. Since I didn’t have it, I simply reused the outer tubing of the USB cable as the protective cover over the soldered wiring.

I should probably still wrap that up with some tape

If you still need some guide on how to do this step by step, here’s one from instructables that you can refer from. While you might not even need a soldering iron or a wire stripper to do this, I personally encourage you to get the proper tooling, even for a simple project like this. A soldering iron kit and a wire stripper isn’t that expensive to own and you will likely need it anyway for future DIY projects.

Soldering Iron Kit

Professional Crimping Multi Tool

Putting it all together

Once you have the cables soldered together, it is as simple as just blue tacking the fan on top of the router and plugging in the USB cable.

Attaching the fan onto the ASUS RT-AX88U just with some blue tack
Powering the fan with the ASUS RT-AX88U’s front USB port
Hiding the cables underneath the router

The Results

With the fan on, the temperatures of the ASUS RT-AX88U’s CPU and Wifi modules drop quite significantly. As you can see on the screenshots below, the ASUS RT-AX88U‘s CPU now averages at around 59°C (138°F) while both the 2.4GHz and 5GHz Wifi modules now averages around 41°C-43°C (106°F-110°F). That’s a 20°C drop in temperature!

Turning off the fan, you can see the temperatures rising pretty quickly too, almost back to the passive cooled temperatures within 20 minutes.

But as for the actual performance of the router, I would have to report that there is no detectable improvements on the transfer speeds on the router. So it really is just to have a peace of mind that you are keeping your router cool at all times, especially here in a tropical climate like Singapore.

All in all, this was still a fun ASUS RT-AX88U related project to hack on a lazy Sunday afternoon. So, if you have a spare 70mm fan lying around, Perhaps you might want to try this mod as well. 😄 And if you don’t have a spare fan, even a cheap Sunon fan like this one below is enough for this project.

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5 Responses

  1. Sandy says:

    Thanks for this article! Try keeping it to suck air out from the bottom instead of the top. That should get your router running even cooler.

  2. xel says:

    I did the same with a 40x40x10mm fan, but instead of push config I have made a pull config, so dust won’t get pushed into the router.

  3. Ken Ng says:

    Thanks for sharing your experience! I actually did a push configuration because I was planning to get a dust filter. This way, with the dust filter, the idea is that only dust free air is pushed into the router, theoratically speaking. I was afraid that a pull configuration may pull dust into the router from below.

    How is the router on your pull configuration, is it relatively dust free?

  4. Richard says:

    Getting my RT-AX88U this week, have already aquired an 80mm AC Infinity USB fan with speed contol for top of router as you correctly did.
    A teardown view of this router shows the heat sinks on the top of the board, not the bottom. I believe Asus designed the case for convective airflow through the front vent, across heatsinks and out the top vent – sucking from the top will enhance the designed air flow and not buck it.
    Forcing air into the bottom might cool some, but really just blows against the bottom of the circuit board.
    Af far as dust is concerned, filters just create problems with extra maintence and inevitable neglect. Pulling air out the top does not avoid dust getting in, as air out means air in somewhere else.
    It is better to take the router outside every now and again and blow it out.

  5. Ken Ng says:

    Thanks for sharing your finding!

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