mrbens

Hi guys, I've just built my first liquid cooled PC with CPU & GPU in same loop. I'm wondering why my GPU always seems to be the same temp as the water (feser one) while the CPU temp is about 20C hotter idle and 10C hotter while gaming?

My setup is TJ07B-W, i7 920 with Heatkiller v3, 4870x2 with Heatkiller X2 block, XSPC360 with 3xYate Loon, XSPC top DDC pump. The mobo is Asus P6TD Deluxe which isn't liquid cooled.

Water temp is checked by inline sensor linked to Sythe Kaze fan controller and ATi Tray Tools to monitor CPU & GPU temps.

Idle: CPU 40-44C, GPU 24-27C
Gaming: CPU 47-52C, GPU 38-40C

Neither are overclocked. Fan RPM always between 750-900RPM to stay silent.

Loop goes Res > Pump > Rad > GPU > CPU > back to Res. GPU first for aesthetic reasons as Rad is on bottom of case so the loop goes in a loop instead of criss crossing!

Is 40-44C idle too high or normal with a GPU in same loop with slow rad fan speeds? Or should CPU be same temp as the water and GPU? Room temp is normally between 19-25C. Might I have applied too much MX-3 to the CPU before seating the Heatkiller v3?

Thanks for any help.

Here's a badly shot pic on my phone until I can borrow a decent camera to show off my baby!

-Ben-

Liability

You just answered your own question. Your GPU is heating up the water before it gets to your CPU. It's to be expected.

KoolMan

lol

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Deviance

Now that your problem is resolved, what kind of cathodes are those? I need pink ones for my build (don't ask).

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Riou

Those are probably UV.

mrbens

I thought with the water temp reaching equilibrium throughout the loop and the temp senser being after CPU & before the radiator cools the water then the CPU shouldn't have a drastically higher temp while the GPU is always same as the water temp.

So if I'd have gone CPU > GPU then the temps would be reversed?

Edit: just seen cathode question. They are Revoltec UV cathodes. They actually look purple but my phone's camera makes them look either red or pink. Can't wait to get some decent pics cos it looks a lot less garish and much prettier in the flesh!

Riou

In your loop, the water that exits your GPU will be warmer than the water that enters into the GPU. You water will be hottest before the rad.

The heat has to go somewhere! That is why you have a rad to get rid of the heat.

mrbens

Thanks for trying to explain this.

It is my understanding that the temp is the same throughout the loop. eg roughly 25C idle with 800RPM fan speed, so if I turn the fans off it will then become roughly 30C throughout the entire loop. That is because the rad fans were cooling the water loop as a whole, not just the water in the rad. The heat is dissapated throughtout the whole loop. That's where the heat goes. The loop as a whole including the rad acts as a giant heatsink.

The water temp sensor being after the CPU and before the rad where it should be hottest should prove this as the temp is same as GPU which is before the CPU.

So this just goes to show that the waterblocks will not always be the same temp as the water, but the water running through them should be. So I shouldn't worry about the higher CPU temps. Is this correct?

Anybody else with GPU > CPU loop can confirm this as normally GPUs run hotter than CPUs? I just want to confirm my Heatkiller v3 is installed correctly.

Thanks,
-Ben-

crazypip666

The water in the blocks absorbs the heat from the component that block is cooling. That heat raises the temp of the water as it passes through the blocks. The water absorbs the heat, so it must be warmer after it passes through the block. The rad does the same thing in reverse.

The heat in the blocks is dissipated into the water, but the heat in the water is only dissipated in the rad, not throughout the whole loop.

I'm not sure how one temperature sensor at the hottest point of your loop shows that the water temp is the same when the water reaches the GPU as it is when it reaches the CPU.

Water blocks will always be warmer than the water running through them or they wouldn't transfer any heat. You should worry about the high CPU temps, and you should swap the CPU and GPU in the loop.

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skkhai

What CPU are you running? Is it overclocked?

I have 2 4870s in the same loop as my CPU. The 4870s have matching temps while the CPU is about 9-10 degrees lower at idle. During games, they're about equal... My cards are the TOP versions, so they're overvolted even in powerplay 2D clocks, I need to try undervolting them when I have time.

Idle, GPU: 36 (Both) CPU: 26
Gaming, GPU: 40 CPU: 38

Try remounting the block and reapplying TIM.

Edit: My loop goes Res > Pump > Rad > Rad > CPU > GPU > GPU > Res.
Edit2: Just reread OP, from what I hear, i7s run hot and your gaming temps look normal.

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