CPU hotter than GPU on combined loop

[hollo]

I'm troubleshooting/installing a watercooled loop, which contains a CPU and a Graphics card, both water cooled.

I don't have a water temperature monitor, but the pipes feel cool to touch throughout. Running the 3dMark TimeSpy benchmark I get a maximum GPU temp of 46C, and a maximum CPU temp of 68C! How can the CPU be 20C hotter than the GPU when they're cooled by the same loop. Does this mean the water block isn't settled on the IHS of the CPU properly, or could there be some other explanation before I take it off and redo the thermal compound etc.?

 

[sepulchre]

Caveat on the below, I’ve only in the last couple of weeks finished my first water cooling loop but experience so far backs up what I’ve read over the last few months

Your CPU and GPU will output different amounts of heat depending upon the workload, if your running something like prime95 that’s going to put a significant load on your CPU and very little on your GPU. It’s unlikely your going to see these components running equal temperatures, you should however see a fairly constant temp of your coolant across your loop as the water flows so quickly it’s not going to become hotter in one place than another.

My 1080 TI Strix OC hits a max of 48 C whilst my 3900x will reach 65 C, when stress testing I’ve been seeing my loop temp, max out at 37 C but this Is higher than I’d like but I’m still playing with fan curves. Im also not happy with my CPU temp but I’m in the middle of a loop strip down and reapplying TIM so hope to drop that a little.

 

[Bugbait]

It's all down to architecture of the silicon, surface area and heat transfer. The heat is more concentrated in a CPU versus a GPU based on surface area per watt of power consumed. The actual CPU core is far smaller than the heat spreader. If you're using an Intel chip, depending on the generation (pre-9k series) then the thermal material between the CPU and heat spreader is garbage. This can add 10C+ to the temperature due to the poor thermal properties relative to solder used by AMD and later generation Intel CPUs.

Short version: Perfectly normal for CPU to be hotter than GPU in a water loop.

 

[pastymuncher]

Hi and welcome to the forums.

As Bugbait states, it's perfectly normal and nothing to worry about. The cpu will always run hotter than a gpu even if you stick a radiator in the loop between them. Loop order is not particularly important apart from needing the res before the pump. Over the 15 years I have been watercooling I have had the cpu before and after the gpu in the loop order and having the cpu after the gpu only adds around a degree to the cpu temps.