Custom loop > AIO and GPU thermals

[Damien.]

Morning,

I’ve got a custom-built closed-loop cooling system in my rig, originally designed to cool both the CPU and GPU. A while back, I upgraded the GPU but didn’t want to install a water block and void the warranty, so I bypassed the GPU connections and kept it on air.

More recently, I upgraded to a 4090—which I’m really happy with and hoping will last me the next 2–3 years. Naturally, it runs hotter than any GPU I’ve had before, so I’ve been experimenting with undervolting. I’ve got it stable at 925mV, but surprisingly, the temps haven’t dropped significantly. That’s led me to take a closer look at the thermal dynamics inside my case.

For reference, my setup is:
Lian Li PC-O11 Dynamic XL
360mm radiator with 3 fans bottom-mounted as intake
360mm radiator with 3 fans top-mounted as exhaust

No additional fans
Side intake area is occupied by a distro plate
Rest of the rig is in my signature

Now, I could be off here, but my thinking is: once the system reaches operating temperature, the bottom intake fans pull cool air through the lower radiator, which heats the air slightly as it absorbs heat. That warmed air is then blown directly onto the GPU, potentially contributing to higher gaming temps and explaining the minimal impact of undervolting.

This has me wondering—would I be better off ditching the custom loop in favor of a high-quality AIO? I’d mount intake fans on the bottom and side (replacing the distro plate), with the AIO and its fans top-mounted as exhaust. While this might result in slightly higher CPU temps, I’ve got plenty of thermal headroom there (currently maxing out at 60°C under load), it could improve overall airflow and reduce GPU temps.

Looking forward to hearing other ideas and thoughts.

 

[pastymuncher]

I did high end custom watercooling of the CPU, GPU and sometimes motherboard (earlier years) for over 17 years but gave it all up around three years ago to go back to air cooling. Due to my own insane attempts to get the best temps from my gpu I ended up putting a AIO on the cpu (reasons explained here). I now have a Lian Li PC-011 Dynamic Evo RGB configured in inverted mode with the gpu mounted in front of the vertical row of fans with three reverse flow fans in the bottom set as intake, a Thermalright Frozen Vision 360mm AIO with the rad mounted in the roof set as exhaust and three Thermalright 120mm fans behind the gpu also set to exhaust. Despite all fans being on my motherboards silent profile I have the best temps on everything that I have ever had while having minimal noise, right now it's completely silent. I have my case sitting on a £5.99 case stand with castors to give extra clearance for the bottom airflow into the case.

For your set up I would do one of four things:-

1. Ditch the bottom rad as that much rad space for just the cpu is a massive overkill and put three reverse flow fans there as intakes which should improve gpu temps.
2. Ditch the custom water cooling, put three reverse flow fans in the bottom as intakes and get a 360mm AIO for the cpu and mount the rad in the roof set as exhaust. Seems silly to do this as you have the components to do this already although you could sell your custom water cooling components and get a 360mm Thermalright AIO for £45 and up.
3. Ditch water cooling altogether and get a £25-45 Thermalright twin tower air cooler such as the Peerless Assassin 120 (less than £24 right now) Phantom Spirit 120, Royal Knight 120 (also less than £24 now), Royal Praetor 130 all of which will be more than enough for your 5800x3d.
4. Either 2 or 3 above plus set your case up so that the gpu is in the vertical position in front of the three side fans with the fans exhausting the heat from the gpu straight out of the side of the case.

 

[Damien.]

SNIP

Thanks for the response.

Inclined to go with option 2. I actually already purchased a AF3 360 AIO for £70. Just trying to decide on the best 120mm fans for bottom (intake) and side.

I was on the fence about completely switching to air as ive read mixed results.

 

[loonyk]

You can try bottom and top intake, side exhaust through AIO.
What are your GPU temps now?

 

[Drumroll]

The Thermalright fan that comes with the Phantom Spirot Evo TL-K12 can be found for just over £8 a piece. Very good fans for the price and minimal RGB, but won’t look silly of left off.
I’m using the Thernalright C12015B 120mm in the Lian Li A3 and they’re very good, but slim fans, OFC.
As others said, AIO is plenty, Air is possible, and custom loop more for looks or very, very, very specific scenarios. Most modern GPUs will be happy with some good airflow and some under volt if needed.
My dive in custom loop was back on the 2700K era, first for looks, later obsessed with temperatures, more often than not, unnecessarily lower than needed. Last GPU I had that a custom loop would make a big difference was the 3090 because of the rear of the GPU. Otherwise watercooling wouldn’t be needed. I was able to tame it with upgraded thermal pads, heat sinks attached to the back plate and direct air flow.

 

[kaku]

2x360mm radiators for a CPU-only loop is overkill. I don't really see a need to buy a separate AIO (unless you really want to). You could take the bottom radiator out and replace it with some fans/ducting to manage the airflow around the GPU area.

 

[Damien.]

I’ve ended up buying the artic liquid freezer 3 pro 360. Got 6 noctua nf-a12x25 and 6 arctic p14 pros. Going to top mount the aio, then bottom and side mount the fans as intake.

Got both fan sets to trial. I’ll try the arctic ones first, if they are good I’ll return the noctuas and save a fortune. If they are as bad as some reviews say I’ll switch out for the noctuas.

Hopefully the arctics will do the job. Will keep the post updated with results.

 

[Damien.]

Update: Thrilled with the outcome!

I've installed the Arctic Liquid Freezer 3 in a top-mounted configuration using the stock fans. For intake, I’ve got three Noctua NF-A12x25s mounted at the bottom, plus another three on the side—all pulling air in.

Thermal performance during a 1 hour Cyberpunk session:

Before: GPU 70°C and CPU 63°C
Now: GPU 60°C and CPU 50°C

I was a bit apprehensive at first since I used the included MX-6 thermal paste with the X application method. Previously, I’d gone with Thermal Grizzly and a spread technique. The MX-6 felt much thicker and more difficult to apply, but surprisingly, it seems to have made excellent contact—core temps are nicely balanced across the board.

Delighted.