I have a Macbook Pro Retina which runs 3 external monitors. Really it runs 4 monitors, because unfortunately it is not possible to conveniently turn off the internal laptop display on OSX and have it remain in that state.
Unfortunately the heat started to become a bit too much for the Macbook of late, with temperatures of 90+ degress Celcius. When it started to get 95 degrees the machine would start freezing up. The only solution would be to unplug all the monitors and take it off the desk. But this was getting a little cumbersome so I set out to find out what else could help with the thermal issues I was having.
I might add that these temperatures were occurring without any erroneous processes eating 100% of CPU, just with my macbook running normally and powering 4 monitors.
Recently I downloaded TP PRO - which gives provides detailed monitoring of your macs system's temperatures.
Interestingly these reported temperatures are approximately 20degrees Celsius hotter than the temperatures reported by smcFanControl. I believe this is due to TG Pro reporting the core temperatures, and smcFanControl reporting the 'CPU Proximity' temperature.
Another useful tool is the Intel Power Gadget which I believe is reporting the CPU core temperature (I have 4 cores, so hopefully it is reporting the highest). The temperature reported by the Intel Power Gadget is inline with the CPU temperatures reported by TG Pro.
I have done a few things to help reduce the temperature. Unfortunately I did not perform these tests with any scientific rigour..but here goes.
At the beginning: my macbook was running a nice 95 degrees CPU core temperature at its highest. I believe I could actually cook food from the 'esc' button to approx F7.
Here is what I tried
Unplugging all external monitors. This definitely helps however if the system is too hot it will remain sluggish.
Number 1 + removing it from the desk. The desk gets hot when running the macbook with 4 monitors, so putting it on another desk (cause the current desk might be 60+ degrees Celcius) does not seem to make a difference.
Blasting my macbook with air through all the ports, around the keyboard and around the air vents at a service station with the old style air pumps. I was surprised how much dust came out around the keyboard. Not much came out the vents however. This seems to reduce the macbook by about 10 degrees. down to approx 80 degrees.
Using smcFanControl to put the fans up to maximum whenever the laptop is plugged in to mains.
I did this only after point III. This drops the temperature a further 15-19 degrees from point III, down to approx 61-65 degrees Celcius.
Using this Targus laptop cooler - fan in laptop cooler letf off - I assumed that this would make a big difference - best case scenario - it makes a 5 degree difference if the temperature is already around the 61-65degree mark. I believe this is because: 1. the surface the macbook sits on now has holes in it to allow better heat dissipation and 2. the surface the macbook sits on is further raised due to the higher rubber 'feet' on the cooler.
Turning the fans on in the Targus laptop cooler made no difference to the temperature of my Macbook.
I am aware there are other things such as replacing the thermal paste and getting a cooling gel pad, but at the moment its comfortably sitting in the low to mid 60's so I am happy.