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Water flow question for new loop


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Hi all!

I am planning to build my very first custom water cooling loop. I see ppl doing the flow like res>pump>gpu>cpu>rad>res. My question is if this setup would hinder the cooling on the cpu? Since it has to go trough the gpu first and move the hot liquid to the cpu from there before go to the rad. Would it be more beneficial (and more expensive :D: ) to build two separate loop or put an extra rad between the gpu and cpu?

 

Thanks

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Hi NosGH,

 

Sounds like you are about to have a fun time. So in my experience the only thing that is important is that you go res>pump. The order of the loop doesn't matter for the most part. Modern PC pumps are so high flow that the loop tends to heat up and cool down all at once, plus or minus a degree.

 

That being said just go with a loop order that looks the best. The most important things to worry about are good thermal paste, pads and fans that have good static pressure.

 

Tip if you don't water cool your Mobo's VRMs. If you overclock use the back fan as an intake to blow cool air over the VRMs. That will help keep them cool and help make your OCs more stable.

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The most you are going to take out of the coolant is one pass through a 280/360mm radiator is about 1-1.5C. So yes, by running from the GPU to CPU you are costing yourself... 1C. But only when under combined CPU+GPU load.

 

I am tedious. I always consider this. I might go CPU -> GPU if I can or bounce to a radiator in between. However, this is all really inconsequential and you should make the best decision in light of your flow pathway, components, aesthetics, or just about anything else. I would not run criss-cross tubes all over just to make it happen.

 

As for two separate standalone loops, this is always going to provide better temps for the CPU in mixed CPU+GPU conditions like gaming and renders. Your specs aren't up there, but your typical CPU might pull 135-200W at full blast. A new 2080 Ti will keep a steady 300W minimum baseline. The CPU usage is far less when gaming and may only run 50-130W as it cycles about. On the other hand, the GPU is pretty steady and consistent. It is the dominant heat source. The GPU is slightly worse off in separate loops. So this comes down to a few key questions:

 

1) Are you going to OC the CPU so close to the edge that an extra 4-5C in coolant temperature (which is +4-5C in CPU temp) will put you over a temperature threshold you cannot tolerate? If no, then your GPU is going to run a lot cooler with dual 280s, dual 360s then if it is tied to just 1x 280/360.

 

2) Can you fit two pumps and if so, will you be OK with increased idle noise from them? Nobody likes the sound of electric pump.

 

From a personal perspective, I have done this both ways on the system in my specs. I started off with 8700K on H115i Pro and Titan XP on a 280mm custom loop. The 8700K is delidded and temps were a laugh at 5GHz, rarely breaking 50C. The Titan was remarkably efficient as well and topped out in the mid 30s at maximum stable clocks. Then I had to go get myself a 2080 Ti. It does pull a bit more power, but the underlying components are less efficient as well. Now my GPU coolant runs 6-8C warmer plus I the GPU chip itself run a good +15-20C over the coolant. Now I have GPU temps in the 50s in Winter. That was not so good, at least from my end. By combining the two components into a dual 280mm radiator, single loop system, they can now dissipate the maximum possible 500W or so through 2x280, instead of 180W/280mm and 330W/280mm. The end result is the GPU temp goes down back to what it used to be, but the coolant temp in the combined loop runs 4C warmer on average compared to the CPU single loop. The larger your CPU power draw, the less beneficial the separate loops are likely to be. If you have a tiny 4 core cranked up to the max paired with a monster GPU, separate loops, even an AIO may be more beneficial.

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  • 2 weeks later...
Thank you guys for the responses. I am still in the research stage. Got everything for my new PC except the CPU/GPU/MB/ram lol. Waiting on the new Ryzen/NAVI/X570 to be out so I am not sure about the power draw yet. My case is the 500d se rgb so I can put a 240 on top and a 360 on front. As for overclocking I have to admit I am in the same shoes as with the custom water cooling ;) Tempting but never did it and would have to do a lots of research before I even dare to try.
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Those leaked 3000 series TDP figures are astoundingly low. Some of that is 7nm platform. Some of it you need to take with a grain of salt. I do think unless you get the 16 core variant, CPU heat dissipation will not be overly concerning. You will have plenty of capacity there, but will be limited at the socket/CPU temp like every other CPU of the last 5 years.
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