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High CPU temperatures with hydro X custom loop

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I have the following configuration


- 1000D obsidian case

- 2x3090 (XG7 waterblock)

- 5950x (XC7)

- XD5 pump/reservoir combo

- Push pull configuration (16 ML in front (intake); 5 on the top for exhaust)

- Soft tubing (no crimps)


Even under regular loads like Overwatch, the temperature shoots up to 88 C. The idle temperature is around 58 C for the CPU. GPU temps are normal at around 34 C idle. I am using Arctic MX4 thermal paste.


Also, I haven't filled the reservoir full (around 1/5 when it is pumping fully).


The pump is running at full speed as well. Any idea on what is causing the temperatures to be so high?

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You need to compare coolant temp vs CPU temp to see where the problem lies. High coolant temp is a water loop problem. High CPU temp with low coolant temp (under 35C) can be any number of things, but most likely the CPU is being kept under load (check Vcore levels) or the CPU block is not mounted properly. One way to check that is quit CUE and see if the load drops.
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If you have things like Precision Boost Overdrive (PBO) enabled, that will certainly push your CPU temperature to 88C. That's actually kind of the point of PBO - it'll auto-overclock your CPU dynamically based on your thermal environment.

Looking at things like the vCore (vCPU in iCUE) is also necessary when talking about CPU temps. More vCore (due to an overclock/PBO) equals more heat.

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Also remember that the bios will push high voltages at idle on Ryzen, close to 1.5V, that's mostly why you see idle temps being much higher than on Intel, even on watercooling.


Have a look if you have bios updates for your motherboard. AMD published AGESA updates not long ago that tame idle voltages a little and may make you save a few °C.


I was wondering when reading your post : You say the reservoir is 1/5 full when the pump is spinning at full speed. Does the level vary depending on pump speed?

If it does it means your rads are probably still full of air and you need to bleed them properly.

Anyway, you'll still want to fill that reservoir up :)


Also, 34°C idle on a 3090 looks pretty poor (unless you have tons of air in the rads and it doesn't cool well), but i suspect you may have the cards set to "maximum performance" in the Nvidia control panel. If you leave power management to "normal", the cards won't keep boost behaviour at idle and that should lower their idle power draw from like 120W to under 40, which will make a substantial difference in idle temps, GPU and CPU since the water will be a lot cooler.

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It boosts up to 1.1 ~ 1.2V and a clock of around 4.5 GHz on all cores. This was after turning PBO off. There are a ton of other OC options I haven't looked up yet so I'll have to look at that later.


One major thing I noticed is that I've swapped the inlet/outlet ports on the CPU cooler (XC7) though I do not know if it should have such an effect on temperature.




@LeDoyen: The GPU temps were high because Nvidia broadcast was running. It dropped to 21C (32C for memory) after I killed that.


As for the reservoir, I didn't fill it fully because at max RPM, it was at that level.


I'll do the following things and report back

- Reverse the direction of the XC7 CPU water cooler.

- Try and bleed air if there's any.

- Connect the coolant temp sensor (got disconnected somehow).


Thanks a lot folks!

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@LeDoyen: The GPU temps were high because Nvidia broadcast was running. It dropped to 21C (32C for memory) after I killed that.


Seems Nvidia's temp reporting is a bit optimistic ^^ on my computer (with 3 sensors on the water loop) it's consistently 1°C lower than water temp at idle. So you water is probably somewhere in the 22 - 23°C which would be great.


So if there's no contact issue between the CPU water block and CPU, that's a pretty steep temperature difference.

Running in reverse flow won't make much difference, you probably won't see any actually, it's very minimal.

I'd bet on either a thermal paste application issue or just PBO doing its magic.

With a 5950X, forget the pea method, you need to spread the paste over all the IHS, because the heat is over the chiplets, on all corners, and to a less extent at the center of the CPU.

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Oh. I made an X with dots in the space but didn't really spread them. Just placed the cooler. One thing is XC7's manual says reversing flow reduces performance (https://www.corsair.com/corsairmedia/sys_master/productcontent/WW_XC7_RGB_SOCKET_115x_AM4_QSG_WEB.pdf ; page 12 FAQ)


Any recommendation on the thermal paste? I'm currently using Arctic's MX4. I'll try reseating it with more thermal paste today first

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For reverse flow they did not state what kind of performance loss you'll experience ^^ it's small. like 1 or 2° at worse.


For paste i usually go with Kryonaut. I find MX4 a bit too thick, this one takes a while to seat if you did put too much. Just personal preference. Thermally, by going to kryonaut i gained a few °C, but nothing to write home about. If you're not overclocking to the verge of thermal throttling, you don't really care about shaving 4 or 5°C.


When you'll remove the waterblock, if you see that the IHS was completely covered, it was okay. too thick will make temps worse. Just make sure you tighten the block gradually in a cross patern to make sure it lays flat on the IHS.


If it's still that hot, you'll know it's entirely due to vcore, and will have to start tweaking a bit with Ryzen master

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