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High CPU temp issue

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Hello all, I have an issue where my CPU is running hot when idle. I installed a hydro x water loop system and am very new to doing this. Here's my setup:


Obsidian 1000d case

1x XD5 pump/reservoir

1x XC7 CPU block

2x XG7 GPU blocks

2x XR7 480mm rads (front of case with 8 fans)

1x XR5 420mm rad (top of case w/3 fans)


PC is powered with EVGA Supernova 1600 P2 80+ Platinum.

CPU: Intel i9-9900k


Pump goes to GPU blocks first, then to CPU, to the 420 rad, then to the 480 rads before back to the reservoir.


As far as I can tell, my coolant temp is low but my CPU runs high and low loads or just doing nothing. I tried replacing the thermal paste with ARCTIC MX-4 - Thermal but that didn't help. I think the coolant if flowing well but I noticed there is usually an air pocket coming "out" of the 420mm rad. Not quite sure how to get rid of that and if that is the culprit to my problem. Anyone have a ideas?


Here's what icue is showing me:


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This has to be poor contact between CPU and XC7 block. There is no way a 9900K with any kind of conductive cooling should hit 80C at less 1.00v.


This should have been visible on the CPU block with a large chunk of unspread (melted) TIM. Usually suspects are mounting posts that don't go through the MB to the backplate quite right, a spring in a bad position, or overly tightening one corner before the others. The TIM spread might give you a clue as to which of the 4 corners to look at.

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I dabbed on some paste and tried to make sure the 4 screws were the same pressure. Temp certainly shows better, but for idle I'd expect it still to be lower. I'm not overclocking so not sure why it's so hot.


Here are two sensor shots at different vcpu




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eh, not really idle, you have something constantly pushing the CPU close to 10% usage. that won't help.


there's no air in the loop? the 1000D is a bit of a nightmare to tilt to help fill those rads, but the 40° on the 2080 kind of bothers me. when the card is idle it's often almost at water temp.


If you are using the HydroX profiles for the pump, it may be spinning way too slow. maybe try a fixed speed like 70% PWM or 3000 RPM, see if the idle temps shoot down.


either way it would be better to create you own speed curve. iCUE doesn't know how restrictive your loop is, so you'll have to tune your pump speed to still get a good enough flow.

Usually a good starting point is 50% PWM at idle and somewhere like 60 - 75% under load, then fine tune to taste

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There's definitely some air in the loop. I've been trying to get it out but it really is a pain. I mostly notice the bubbles in the outtake of the upper rad and some in the cpu block. I try tilting but this thing is really heavy. I also do have a custom curve. Sometimes I try cranking it to 4900 to try to get the air bubbles out. Should I take the cap off the reservoir to help remove the bubbles?





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You should set the pump and fans to be controlled by the water temperature, that will save you quite some noise from them accelerating and slowing down contantly :)

there's no point in accelerating instantly since the water is still cold, there's nothing to dissipate.

the water will absorb the heat from the little spikes of usage, and warm up very slowly.



Regarding air bleeding, there's no need to remove the cap. if air moves out of the rad, it's because water moves in :) . you'll just see the reservoir level go down little by little, and will have to top it up until all the air has been removed.


you could make the pump run faster to start with. with 3 big rads, the water flow is reduced quite a bit.

to give you an idea, running 3 rads too, i start to hear bubbles move only above 70% PWM, and to dislodge them, i have to leave the pump at 100% for a few hours sometimes.


Try filling your reservoir to the very top, and setting the pump to 100% and leave it like that while you use it.

it's all soft tubing, no 90° fittings.. maybe the flow will be high enough to work the air out on its own (and will save your back!)

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This seems better on temps and 69C at 1.2x volts is in the right neighborhood. The 82C at idle Vcore was a clear warning sign even if that was a moment of transition.


As to bubbles… that last small one in the top of the cpu block is always stubborn. Tipping the case while running will work, but not for the faint of heart. Another thing to try is pulse shifting from a low to maximum rpm. Set a custom curve for the pump and then set a very low 1000 rpm or so fixed speed. Then change it to 4800 rpm (or 25% to 100% PWM) and let it run for 10-15 seconds before dropping back to low for 5 seconds and repeating the process. The surge can help push that out, but it reliant on pressure. More difficult in a high resistance system. 3 blocks + 3 rads qualifies.

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Yeah that big bubble there on the outflow of that radiator needs to go. I know the case is heavy but try and rotate it all around while running the pump at 100%. It would also be nice to know the flow rate in a loop with that much rad and blocks considering you only have one pump.
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  • 2 weeks later...

Ok I wanted to give an update on this. I drained the fluids and redid the loop. Now it goes Pump > GPUs > Upper Rad > CPU > Front Rads > Reservoir. I replaced the XC7 CPU block with the newer one (M3 Gen 2) and used new coolant. I also added a couple thermaltake temp/flow monitors. Now my CPU runs at 35C idle and pops up to 55-60C when running a game. Bubbles are back in the CPU block so I gotta work those out, but overall am happy with the improvement. I'm guessing it was both the flow and the coolant which was roughly a year old. Replacing the CPU block might've been overkill but I didn't care at this point.


Thank you everyone for the responses and advice.

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