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?