Hello.
I've been building and developing on computers my whole life. But, this is my first try at a water cooled build. So, I'm learning as fast as I can, as I go.
My system is all put together and running. But, when I put the machine under load (playing Alan Wake 2 at high quality) the water temperature quickly (within 5-10 minutes) climbs to 40 C and triggers the alarm in my D5 Next pump.
So, this raises a question:

Is 40 C a good alert number? My GPU and CPU (both water cooled) seem to be at good temperatures. So, I'm not certain if 40 C is just a conservative default or if I should be shooting for lower water temperature?
Assuming that 40 C water temp is a sign of trouble, what do you recommend as my next steps to troubleshoot? (I have theories and observations. But, I think I need expert guidance or I could waste time checking irrelevant things)
These are the parts I'm using:

ASRock x870e Nova Motherboard
9950x3d CPU - Water Cooled with a cuplex kryos NEXT with VISION AM5/AM4, copper/copper
PNY RTX 5090 GPU - Water Cooled with an Alphacool Core waterblock
(The TDP for this CPU+GPU is 745W)
Pump & Res - ULTITUBE D5 200 PRO expansion tank with D5 NEXT pump
Radiators - 2x 360mm Heatkiller
Radiator Fans - Asus Rog Strix xf120
PETG 10mm/12mm tubing - No radical turns or super long runs. Short runs with only 90 or 45 bends.

Any help would be greatly appreciated!

Zitat von »Remayz«

with two 360mm rads and the components you have, maybe raise the alarm temperature to 50°C and try to keep the water temp below that.
I just saw you have PETG tubes, so yea, try to keep the water temp below 50°C at all times
with such power hungry components, i don't think 40°C is a realistic temp on dual 360 unless you don't mind a lot of fan noise. It's too easy to reach the 40s even with more radiators.

Thank you for this. I don't mind getting an additional radiator if thats what the components call for. Planning the system, I got mixed input with most sources suggesting that 2x 360mm would be more than enough.
My humble theories:
1) A flow obstruction. The water looked very still and I was getting very different water temp reads between pump sensor and cpu sensor. I don't have a flow sensor installed (aquacomputer flow next is in mail to me now).
2) Air-starved radiator. I mounted one of them on the bottom of the case and there are 3 layers of screen, grill and fan-frame structure in its way.
3) I just need more radiator for the heat those devices put off. I could see that the CPU was 100W and GPU was at 575W during load. And I do not like fan noise at all!
I drained the system and have taken everything apart. Cleaning and looking for obstructions.
But, your vote is for adding another rad? Anyone else concur or have a different item to check?

I can't find the RPM in my notes and its all taken apart now. But, the pump was running at 80%.
Strangely, changing the pump from 50% to 80% didn't seem to affect the issue at all.More efficiency at higher rad temp does sound familiar. When I had the fans at 100% (~1750rpm) and the pump at 80%, the water temp would start climbing quickly. But, would slow down just before 40 C. It looked like it was going to plateau around 40 C in those conditions. But, I stopped it before the 40 C alarm because I was worried something could get damaged.

Today, I drained it and took the entire loop apart. I flushed everything. Some debris could have washed out that I didn't see. But, I did notice a few things:
A) There was a metal shaving from the port screw tapping in the GPU block. Removed.
B) The GPU block is way more constraining on flow than the other parts. The path and outlets are very narrow.
C) I hadn't seen that there is an "IN" and "OUT" port on the GPU block (its etched into the plexiglass faintly). Of course, I had it the wrong way. So, not sure how badly that would hurt flow?

I'm going to put it back together with a Flow Next integrated and both 360mm radiators at the top of the case. With everything flushed and those changes I'm hoping it cools better. If not, I will at least have more information. Plus, I'm building the loop in a way that leaves part of the case open for another 360mm.And I guess I may need a second D5 Pump?

Quoted from "Remayz"

don't worry for nothing
40°C is nothing to be scared of. most people will probably have their system running water temps around thet 45 ish °C. when you start reaching the 50s, you can start worrying a bit or start tweaking fan curves.

Watercooling hardware usually have a maximum operating temperature of 60°C.

With PETG tubes you don't want to get near that but you're not likely to get there already with two rads.

More waterflow does not help cooling. As long as you have enough flow for the waterblocks to effectively remove heat, you're fine, and that happens at pretty low flows. the D5 at 50% would be more than enough already with the config you have.
While you wait for the flowmeter you can have a play with it by watching y our GPU temperature under load and playing with the pump speed.
When it runs really slow, there's a threshold where you will see the GPU temp shoot up 10-15°C pretty sharply.
Speed up the pump slowly and it will fall back down just as fast..that'd be your minimum pump speed for the waterblock you have.
Typically, between that speed, and 100%, you shouldn't see too much dfifference.

My apologies for the delayed follow up. I had taken apart the PC and needed to wait for parts to be shipped to get it going again. My other PC options were out too. So, I was down to my phone.
My report:

A) With the Flow Next in, I'm seeing around 140 l/h with pump at 50% and 205 l/h when it's at 100%.
B) Just as you said, going from pump 50% to 100% does not seem to lower water temp. In fact, it jumps up, I believe due to increased pump heat, and then slowly crawls back to where it was at 50%.
C) With this new configuration, I'm getting water temps capped at around 35.5 C. Even at full load, 700 W or so, it doesn't typically go above that. BUT, that is with fans at 100% and pump at 50%.
D) I'm fairly convinced that the primary cause for the improvement was correct bleeding. During my last testing, I did some gentle bleeding, tilting the case, etc. But, its a huge case that easily weighs 75lbs. So, I didn't really rotate it all the way around. When I did so this time, I found that quite a lot more air escaped. So, I'm pretty confident that my earlier, over 40 C results were due to huge air pockets left in the rads.
All this being said, I'm happy to have a functional machine with temps under control. And its extremely quiet when not under load. But, my goal was for quiet even under load. Otherwise, I could have just stuck with air cooling.
So, I now have a 3rd radiator on the way. I'm adding a 360mm Hardware Labs GTX. I'm hoping that allows me to run the fans lower than 100% during load.
Of course, the next problem with a 3rd rad will be flow. So, I'm already thinking about adding a 2nd D5.

Quoted from "Taubenhaucher"

I don't think you need to worry about the flow rate. I have four 420 radiators in my system and achieve 120 l/h at 60% power of the D5NEXT. Even if the flow rate drops due to the additional radiator, it won't drop so far that it affects the water temperature.

Ah. Great to know. I've already extended this project too much. I'm guessing that I'll be around 120 l/h at 50% with the added rad.

Quoted from "Bartdude"

You didn't mention what your ambient room temp is, this will directly affect the temps inside the PC. Lower = better. This is why sever rooms etc. all have air con.

Good point. Makes sense. It's in a house with A/C. So, the room probably hovers around 24-25 C.
I have thermal sensors just outside of the fan intake areas. For some reason, they measure a little higher than expected. They tend to be around 26-28 C.