Alarming GPU temperatures, low CPU temperatures

Discussion in 'MacBook Pro' started by Teuthos, May 8, 2015.

  1. Teuthos macrumors member

    Mar 21, 2014
    Yes, I know that Apple has thoroughly tested their products and running a CPU at 90-95 degrees and a GPU at 75-80 degrees is perfectly safe, and that high fan speed will not significantly lower the lifespan of the fans, and that usually there is no reason to worry about temperatures. However, there has recently been a worrying change, for no apparent reason, in the thermal performance of my computer, which is what this thread is about.

    When I first got my late-2013 15'' rMBP, the CPU temperatures would regularly exceed 90 degrees Celsius and the GPU would stay nicely under 80 degrees, usually with quite slow fans (3000-4000 rpm). Occasionally, when needing to complete intensive tasks on battery, or when doing long intensive tasks in the background and not wanting to hear the fans all the time, I would use Turbo Boost Switcher to turn off turbo boost on the CPU - this would keep my CPU temperature at around 70-75 degrees and the fans off.

    Recently, however, I have noticed something strange. First of all, the CPU temperature never rises above 80. Never. I even tried running Prime95; the overall CPU temperature (which smcFanControl shows) never went above 75 degrees Celsius, though the individual CPU cores were in the 94-98 range according to iStatMenus. Previously smcFanControl would show 90-95 degrees for the overall CPU and the cores would be at 95-100 degrees. Now, cooler temperatures are always better, but this is confusing. Perhaps Turbo Boost Switcher permanently stopped the CPU turbo boost for some reason?

    The worrying part is that the GPU temperatures have suddenly taken a rise. Previously it was difficult to get the GPU temperature over 80 in anything; now it will easily stay in the 84-86 degrees range even with the GPU fan at full speed (5700 rpm) when playing games. However, for some reason the Unigine Heaven benchmark, which makes the whole computer sluggish, will not raise it further than 80. Also, even when only the iGPU is running, the GPU temperature heats up faster than the CPU. Why is this?

    Perhaps I'm overthinking things, but this seems very strange to say the least. So to summarise, my questions are:

    1. Is running a GT 750M at up to 85-87 degrees Celsius several hours a day going to significantly affect the system's lifespan or cause damage? I intend to keep this computer for a long time.
    2. Is there a free Mac application that lets me see the CPU's clock speed to ensure that turbo boost is working as intended?
    3. When people talk about CPU temperatures, are they talking about the core temperatures or the overall CPU temperature (what iStatMenus calls "CPU Proximity"
  2. leman macrumors G3

    Oct 14, 2008
    Did the GPU benchmarks improve for you? This just sounds as a slight tweak of SMC.
  3. Teuthos thread starter macrumors member

    Mar 21, 2014
    The Unigine Heaven GPU benchmark showed a negligible difference of 0.9% (downwards) when I ran it again, from 919 to 911 with the basic preset, so performance-wise the GPU performs identically.
  4. Teuthos thread starter macrumors member

    Mar 21, 2014
    I found a handy utility called Intel Power Gadget and ran the Prime95 test in the background.

    The CPU clock speed was in excess of 3 GHz for several seconds before slowing down and keeping at 2.5 GHz. The program indicated the CPU temperature that was close to or equal to the CPU PECI die in iStatMenus - around 90-100 degrees at max load. I'm still confused as to whether it is the CPU core / CPU PECI die temperature or the CPU proximity temperature provided by smcFanControl that people use when talking about CPU temperature.

    A stable 2.5 GHz also seems quite low; it appears that the CPU is barely turbo-boosting. Is it normal?
  5. snaky69 macrumors 603

    Mar 14, 2008
    A CPU will turbo boost whenever it has the thermal overhead to do so. Whenever temps are too high it'll throttle back to normal speeds, and if things particularly toasty it'll throttle back even more.
  6. chevalier433 macrumors 6502a


    Mar 30, 2011

Share This Page