Higher case fan speed = higher GPU temperatures

[Lare111]

I have an i7-11700F and an RTX 3060 Ti in a Phanteks P300A case. The case is equipped with 3 x Be Quiet! Silent Wings 3 120mm fans. They are actually very good fans. Quiet, good looking and have decent static pressure for the front mesh panel. I have blocked the top fan place with sound dampening material since it reduced noise levels considerably and didn't affect temps. However, the GPU has been running slightly hotter than I would have thought and removing the side panel always reduces the temperature. My GPU exhausts all the hot air through side vents so the small gap between the GPU and the side panel isn't ideal.

 

Now I did some testing. I had Unigine Heaven running in the sedond monitor and I paused the benchmark in a scenario where the GPU was heavily power limited. I set GPU fan speed to fixed 1500RPM and tested different case fan speeds in Argus Monitor. I noticed that the faster I run the upper front fan which cools the CPU, the hotter the GPU runs! These are the results:

 

Fan speed 1500RPM = GPU temperature 75C

Fan speed 1000RPM = GPU temperature 72C

Fan speed 0RPM = GPU temperature 69C

 

So, what's going on in here? Why does the fan above the GPU affect temperatures so much? I suspect that the upper fan produces airflow which prevents the hot air coming from the GPU from raising to the exhaust fan. Or maybe there's just too much positive pressure in the case which disturbs the airflow. However, the rear of the case is very open and I can feel that there's air coming through.

 

I have circled the fan which causes high temps.

 

[creesch]

That's odd indeed, you would think the lower fan is causing it by blowing air past the GPU intake 

[DoctorNick]

Clockspeed. What Boost clock at 72c vs 75C? Maybe gpu is boosting higher.. More airflow = lower temp. You can check CPU temp to see if this is true

[Lare111]

Just now, DoctorNick said:

Clockspeed. What Boost clock at 72c vs 75C? Maybe gpu is boosting higher.. More airflow = lower temp. You can check CPU temp to see if this is true

GPU was hitting the 216W power limit constantly during the paused benchmark so it can't really produce any more heat. Clock speed was pretty stable 1935Mhz.

 

I'm still running tests and no matter how slow I run the upper front fan, it always increases GPU temps. That's just so weird.

[Alder Lake]

2 hours ago, Lare111 said:

I have an i7-11700F and an RTX 3060 Ti in a Phanteks P300A case. The case is equipped with 3 x Be Quiet! Silent Wings 3 120mm fans. They are actually very good fans. Quiet, good looking and have decent static pressure for the front mesh panel. I have blocked the top fan place with sound dampening material since it reduced noise levels considerably and didn't affect temps. However, the GPU has been running slightly hotter than I would have thought and removing the side panel always reduces the temperature. My GPU exhausts all the hot air through side vents so the small gap between the GPU and the side panel isn't ideal.

 

Now I did some testing. I had Unigine Heaven running in the sedond monitor and I paused the benchmark in a scenario where the GPU was heavily power limited. I set GPU fan speed to fixed 1500RPM and tested different case fan speeds in Argus Monitor. I noticed that the faster I run the upper front fan which cools the CPU, the hotter the GPU runs! These are the results:

 

Fan speed 1500RPM = GPU temperature 75C

Fan speed 1000RPM = GPU temperature 72C

Fan speed 0RPM = GPU temperature 69C

 

So, what's going on in here? Why does the fan above the GPU affect temperatures so much? I suspect that the upper fan produces airflow which prevents the hot air coming from the GPU from raising to the exhaust fan. Or maybe there's just too much positive pressure in the case which disturbs the airflow. However, the rear of the case is very open and I can feel that there's air coming through.

 

I have circled the fan which causes high temps.

 

are you sure that fan in the back is acting like an exhaust? it could be going against the fan in the front, causing hot air to build up in the center of the case, unable to escape

[Lare111]

23 minutes ago, Alder Lake said:

are you sure that fan in the back is acting like an exhaust? it could be going against the fan in the front, causing hot air to be stuck in the center of the case

It's definitely exhausting. It's visible in the picture too since the fan frame points backwards.

[Alder Lake]

Just now, Lare111 said:

It's definitely exhausting. It's visible in the picture too since the fan frame points backwards.

how about the fan on the CPU cooler

[Lare111]

29 minutes ago, Alder Lake said:

how about the fan on the CPU cooler

It's blowing in the same direction as case fans.

[Alder Lake]

46 minutes ago, Lare111 said:

It's blowing in the same direction as case fans.

I can't explain it easily then, it is possible that due to how the heat sink is set up in a way that pushes air down instead of backwards out the case, so that more airflow is worse for the GPU, or it could be that there's hot air in front of the PC being drawn in by the fan, or it could be turbulence between the 2 fans at the front which is worst at higher RPM, or one of the fans could be backwards, there's a million things that could be wrong

 

if the CPU gets cooler while the GPU gets hotter, it could be somehow pushing the CPU air down to the GPU, but I don't see exactly how that's possible

[aisle9]

Ok, I'm not a meteorologist, but I did hang out with them a lot back in the early 2010s, and this would be my guess: the higher airflow from the upper fan is drawing the slower airflow from the bottom fan into it, pulling air away from the GPU. High pressure/low pressure thing. The slower airspeed on the bottom creates an area of higher pressure compared to the faster airflow up top, and air wants to move from high pressure to low, so it's getting pulled up there rather than straight back.

 

Try this: adjust the speeds on your top inflow to match your lower inflow (or the other way around), then crank up the speed on your exhaust a little. If it is just the airflow differential causing it, you should see a difference.

[Ralfi]

I was going to suggest the sound dampening may be impacting things but you said it didn’t change temps. 
 

Have you matched the two front fan RPMs? What’s the lower front RPM whilst you tweak that of the upper front fan?

 

Can you set the lower front fan to be controlled by the GPU temp - so it’s not running at high RPM all the time - to see if that changes anything?

[Lare111]

Sorry for the late reply. I couldn't figure out the issue on the Phanteks P300A so I bought the Fractal Design Meshify 2 Compact instead. CPU temps are so much better now and GPU also runs couple degrees cooler. Now I have 3 x 120mm front fans blowing cool air in to the case so both GPU and CPU get enough fresh air. Only one 120mm rear fan seems to be enough for exhaust since positive air pressure pushes hot air out through top and rear.