Cpu temperature fluctuations?

[RaymondSWalters]

Hi there!
Just a quick quistion...
I have the i7 4790k 4.4GHz cooled by the corsair H110 and arctic mx4 paste and my gpu R9 280X cooled by thermaltake water 3.0 pro and arctic mx4 paste.
Under gpu stress tests i notice that my gpu temp goes up slowly to 55C max and if there are no gpu processes it cools slowly to 30C idle
But
When i run cpu stress tests my cpu temps go from idle 35C (it is summer here) immediately (after i press start in the stress test) to 65C ( and stays there for hours...) . And when i press stop the temps immediately fall back to 35C
This surely cannot be accurate
Can someone please explain this?
Thanks in advance!

Ps. I use open hardware monitor for both cpu and gpu temp monitoring

 

[Jared Jensen]

When your CPU and GPU are being utilized a lot, the temperatures will increase because more heat is being generated. It's perfectly normal to have those temps under load.

 

[Solandri]

Your i7 has a die size of 177 mm^2, about a third of which is the iGPU you're not using.
http://images.anandtech.com/doci/7003/Screen%20Shot%202013-05-31%20at%207.59.16%20PM_575px.png

Your R9 has a die size of 352 mm^2, and nearly all of it is used when you run a game.
http://images.anandtech.com/doci/7457/HawaiiArch.png

So it would make sense that the video card takes a lot longer to cool down. It simply has a lot more "stuff" which has heated up.

 

[RaymondSWalters]

When your CPU and GPU are being utilized a lot, the temperatures will increase because more heat is being generated. It's perfectly normal to have those temps under load.

I know that
What i don't understand is why my cpu temps climb/drop 30C almost immediately according to the utilization while my gpu temps don't

 

[RaymondSWalters]

Your i7 has a die size of 177 mm^2, about a third of which is the iGPU you're not using.
http://images.anandtech.com/doci/7003/Screen%20Shot%202013-05-31%20at%207.59.16%20PM_575px.png

Your R9 has a die size of 352 mm^2, and nearly all of it is used when you run a game.
http://images.anandtech.com/doci/7457/HawaiiArch.png

So it would make sense that the video card takes a lot longer to cool down. It simply has a lot more "stuff" which has heated up.

I understand that but still 30C in 5 seconds just doesn't feel right

 

[thebest21445]

Your i7 has a die size of 177 mm^2, about a third of which is the iGPU you're not using.
http://images.anandtech.com/doci/7003/Screen%20Shot%202013-05-31%20at%207.59.16%20PM_575px.png

Your R9 has a die size of 352 mm^2, and nearly all of it is used when you run a game.
http://images.anandtech.com/doci/7457/HawaiiArch.png

So it would make sense that the video card takes a lot longer to cool down. It simply has a lot more "stuff" which has heated up.

I understand that but still 30C in 5 seconds just doesn't feel right

it is because after you are stress testing the cpu the cpu cools down because it is still being cooled down by your watercooler and it will instantly fall down to 30c because it is still being cooled as i said. its like taking a hot chocolate and after it is hot you put like 5 ice cubes on it and it instantly cools down. just like your cpu. happens to me too so its all normal. this should be happening.