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Higher Temps in High Performance Mode

TheBuffather

TheBuffather

macrumors 6502a
Original poster
Jul 19, 2009
515
282
Tampa, FL
Hi all,

I have a late 2008 MBP 2.66GHz w/4GB ram. When I turn on the high performance mode, I notice that my CPU temp goes from around 73C to close to 85 or 90C and my fans start to kick it up a notch. Is this normal? I've Googled around a bit and can't find a true explanation as to why this might occur. My logic tells me that the CPU would be used less due to the GPU being turned on and utilized. Am I missing something?

Thanks!
 
If the GPU is being used more, wouldn't that contribute to your higher temps? Perhaps the GPU raises the temperature inside the case or something. I just did some googlin' on this issue for my friend who is having the same problem, and that's the only thing I could come up with. Seems to be the same idea that other people have as well...
 
JBuff88 said:
Hi all,

I have a late 2008 MBP 2.66GHz w/4GB ram. When I turn on the high performance mode, I notice that my CPU temp goes from around 73C to close to 85 or 90C and my fans start to kick it up a notch. Is this normal? I've Googled around a bit and can't find a true explanation as to why this might occur. My logic tells me that the CPU would be used less due to the GPU being turned on and utilized. Am I missing something?

Thanks!
Click to expand...

More power available = more heat, why don't people grasp this simple concept?

What are you running to get things this heated up?
 
snaky69 said:
More power available = more heat, why don't people grasp this simple concept?

What are you running to get things this heated up?
Click to expand...

Hmm, well I'm sorry that I have seemed to annoyed you. However, I specifically stated that my CPU gets hotter; not the GPU. I can understand the GPU warming up, but that's not really the case. As soon as I log in while on High Performance mode, the CPU starts to run in the 80s or 90s.

I am not running anything to get it all heated up; that's the thing. I can start the computer up and then let it sit there with nothing open except Flu.x and a small menu weather app, and the CPU will heat up to the mid 80s. Normally, in low performance mode, the CPU barely reaches 50C while using only Safari.

This is why I am so confused with the high temps in the high performance mode. This doesn't seem like it would be normal, especially with the CPU rocketing up right from the very start.
 
The GPU consumes a lot of power when you turn it on (and anything that consumes power produces heat.)

This is why the GPU is off when not in performance mode.
 
So the consensus is that it doesn't seem odd to anyone here that turning the GPU on will cause the CPU itself to increase heat by 35-40+ C? That just seems extraordinarily high to me. I understand that there should be somewhat of an increase in temps, but I didn't think it would be that much.
 
JBuff88 said:
So the consensus is that it doesn't seem odd to anyone here that turning the GPU on will cause the CPU itself to increase heat by 35-40+ C? That just seems extraordinarily high to me. I understand that there should be somewhat of an increase in temps, but I didn't think it would be that much.
Click to expand...

35-40 degrees? Yeah, that would be odd with all things equal. But your original post mentioned a 12-17 degree increase.

You are changing the ambient temperature within the casing, so you are going to see some increase.
 
getz76 said:
35-40 degrees? Yeah, that would be odd with all things equal. But your original post mentioned a 12-17 degree increase.

You are changing the ambient temperature within the casing, so you are going to see some increase.
Click to expand...

The 35-40 degrees is from a dead start up, as I was mentioning in my previous post. I think I am going to take in my MBP to Apple and see what they say.

Thanks for the help everyone.
 
JBuff88 said:
So the consensus is that it doesn't seem odd to anyone here that turning the GPU on will cause the CPU itself to increase heat by 35-40+ C? That just seems extraordinarily high to me. I understand that there should be somewhat of an increase in temps, but I didn't think it would be that much.
Click to expand...

73 to 90 degrees is not 35-40C. it's 17C, which seems completely acceptable.

even from startup, it's gonna idle 40-60 degrees, depending on your CPU.
 
JBuff88 said:
Hmm, well I'm sorry that I have seemed to annoyed you. However, I specifically stated that my CPU gets hotter; not the GPU. I can understand the GPU warming up, but that's not really the case. As soon as I log in while on High Performance mode, the CPU starts to run in the 80s or 90s.

I am not running anything to get it all heated up; that's the thing. I can start the computer up and then let it sit there with nothing open except Flu.x and a small menu weather app, and the CPU will heat up to the mid 80s. Normally, in low performance mode, the CPU barely reaches 50C while using only Safari.

This is why I am so confused with the high temps in the high performance mode. This doesn't seem like it would be normal, especially with the CPU rocketing up right from the very start.
Click to expand...

They are right next to each other, effectively heating each other up. Your temps do seem out of the ordinary for a computer simply idling.

Give resetting the SMC a try, and if that doesn't work, I think it deserves a little visit to your local Apple Store or reseller for a checkup.
 
here's how it works.

let's say ur not using the discrete GPU and the CPU is doing majority of minor graphic related tasks... in this case, majority of the heat would be caused by the CPU and that heat would be transferred to the heat sink... the fan would turn on and cool down the CPU.

now let's say you put it in high performance mode... this would in effective "turn on" the GPU and move the graphic related task to the GPU instead of the CPU, but CPU is still working but not as hard. the GPU will now output additional heat along with the CPU. KEY THING HERE is that the GPU and CPU are on the same heat sink. Once the GPU outputs more heat, and the CPU is no longer doing graphic related tasks, even if the CPU temps go down, the GPU will have already made the heat sink hotter. if the CPU cools down, the hot heat sink will transfer some of the heat to the CPU. (i.e., if the heat sink is 80C bc of the GPU, and currently the CPU is around 65-70C, the heat will unavoidably transfer a bit to the CPU, there by causing the temp to rise = CONDUCTION)

Conduction: Heat spontaneously flows from a region of higher temperature to a region of lower temperature, temperature differences over time, approaching thermal equilibrium.

edit:
not to be boasting or anything, but i did major in physics in undergrad. [but now working in finance]
 
The GPU and CPU in the Macbook Pro 15's use the same heatsink. Naturally, as the GPU heats up, the heatsink is unable to cool the CPU effectively, so both gets warmer.

u4J1pPwXHUrWNNqf.huge
 
head honcho 123 said:
here's how it works.

let's say ur not using the discrete GPU and the CPU is doing majority of minor graphic related tasks... in this case, majority of the heat would be caused by the CPU and that heat would be transferred to the heat sink... the fan would turn on and cool down the CPU.

now let's say you put it in high performance mode... this would in effective "turn on" the GPU and move the graphic related task to the GPU instead of the CPU, but CPU is still working but not as hard. the GPU will now output additional heat along with the CPU. KEY THING HERE is that the GPU and CPU are on the same heat sink. Once the GPU outputs more heat, and the CPU is no longer doing graphic related tasks, even if the CPU temps go down, the GPU will have already made the heat sink hotter. if the CPU cools down, the hot heat sink will transfer some of the heat to the CPU. (i.e., if the heat sink is 80C bc of the GPU, and currently the CPU is around 65-70C, the heat will unavoidably transfer a bit to the CPU, there by causing the temp to rise = CONDUCTION)

Conduction: Heat spontaneously flows from a region of higher temperature to a region of lower temperature, temperature differences over time, approaching thermal equilibrium.

edit:
not to be boasting or anything, but i did major in physics in undergrad. [but now working in finance]
Click to expand...

syan48306 said:
The GPU and CPU in the Macbook Pro 15's use the same heatsink. Naturally, as the GPU heats up, the heatsink is unable to cool the CPU effectively, so both gets warmer.
Click to expand...

Ah! Thank you to you both. This makes a lot more sense to me now that you have explained the heat sink design. I REALLY appreciate the help!
 
Not to sound stupid (still new to Macs) but how do you turn it to High Performance mode? I'm running Lion.
 
saberahul said:
Not to sound stupid (still new to Macs) but how do you turn it to High Performance mode? I'm running Lion.
Click to expand...

You can't. This was only for older MBP's that didn't have automatic graphics switching. You had to switch to high performance or power saver, then log out and back in for it to take effect.

In your case, you probably have the newer 2011 MBP which does this automatically, there is nothing for you to set.
 
snaky69 said:
You can't. This was only for older MBP's that didn't have automatic graphics switching. You had to switch to high performance or power saver, then log out and back in for it to take effect.

In your case, you probably have the newer 2011 MBP which does this automatically, there is nothing for you to set.
Click to expand...

Great, thanks for letting me know.
 
snaky69 said:
You can't. This was only for older MBP's that didn't have automatic graphics switching. You had to switch to high performance or power saver, then log out and back in for it to take effect.

In your case, you probably have the newer 2011 MBP which does this automatically, there is nothing for you to set.
Click to expand...


Oh snap. I didn't realize that the newer macs even had graphics card switching. I was wondering what gfxCardStatus was used for... now I understand. Thanks for the heads up!
 
JBuff88 said:
Oh snap. I didn't realize that the newer macs even had graphics card switching. I was wondering what gfxCardStatus was used for... now I understand. Thanks for the heads up!
Click to expand...

Well, the 15's and 17's do, the 13 inches doesn't as it only has the 3000HD, but you still get the point.
 
snaky69 said:
You can't. This was only for older MBP's that didn't have automatic graphics switching. You had to switch to high performance or power saver, then log out and back in for it to take effect.

In your case, you probably have the newer 2011 MBP which does this automatically, there is nothing for you to set.
Click to expand...

snaky69 is right.

but you still can force which graphics chip to use by using gfxCardStatus.

great app... for example... spotify & 1password uses coregraphics and turns on ur discrete GPU (i.e., AMD and not intel 3000)... but in my opinion those apps don't need the discrete GPU so i force my OS to use the integrated GPU (intel 3000) through gfxCardStatus. [uses less electricity and less heat in my opinion]
 
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