I have Dell i7 8850U laptop with 4GB 940MX GPU.
It was heating probably more than normal (CPU cores around 95+ °C, GPU 78°C) during playing games like GTA V.
And my GPU core clock won't go above 405 MHz while playing GTA V as shown below (the photo is little blurry but you'd notice the GPU temperature. It is from Open Hardware Monitor)
Then I just replaced thermal paste.
After that I tried same games.
Observation after thermal paste change:
I noticed that CPU temperatures were not going above 85°C. I also noticed GPU temperatures were not going above 72°C now (previously it was 78°C)
So I assumed thermal paste and cleaning my laptop fan made some positive effect.
Effect on the games:
Light weight games like Counter Strike made no difference. They were very smooth and GPU won't go above 57°C.
GTA V - I noticed GPU core reaching above 405 MHz. It reached around 950 Mhz which made me happy.
However, the higher MHz kept fluctuating. I mean, game runs at around 950 Mhz for few minutes and then next 1 or 2 minutes it will go down at 405 MHz.
The game ran always at 405 MHz before thermal paste change so I never noticed fluctuation. It was slow but no fluctuation.
And it continued like this. Stats on same are given below.
Open Hardware Monitor Stats:
I noticed interesting observation.
When the GPU was at 405 MHz, its temperature was around 66°C. CPU core clocks were around 3300 MHz
When it was around 950 Mhz, the temperature was around 70°C. CPU core clocks were around 2500 MHz
My overall observation and conclusion:
The thermal paste probably fixed temperature issue but this fluctuation problem is related to either CPU clocks or GPU being given less power. So it runs at 405 MHz from time to time because GPU temperature is slightly low - 66°C. Low power == less temperature?
Similarly, when MHz reaches 950+, the temperature also reached 70°C. More power == more temperature and better performance?
What I tried to fix it:
I tried all power settings in laptop battery settings and NVIDIA power settings in control panel. It probably made no difference.
Then I thought maybe something has changed recently and GPU max temperature has been limited to 72°C and so it can't improve performance at all?
Why I think so is because before I applied thermal paste, the GPU would touch 78°C often (speed won't cross 405 MHz though).
So I used GPU-Z software to see if there' some temperature limit on my 940MX GPU:
It says Current = 70°C. So I feel that is where it is limiting something.
Given all that, what could be the reason of this kind of fixed fluctuation? Is it due to some power issues? Or the game like GTA V too heavy for this processor? So this fluctuation in this game with this processor should be normal?
Or could it be related to some CPU issues too?
EDIT: I further tested and I observed something more focused now. When my laptop charger is plugged in, the CPU temperature will tend to stay between 72-80 C. And GPU clocks fluctuates like I described before.
When I ran the game only on battery and no charger plugged in, CPU temperature tend stay below 70 C. There were almost no fluctuations in clocks. It ran fine on around 915+ clock.
Looks like CPU temperature has a role in the issue. And more specifically, issue is related to power sources - battery vs charger.