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Short answer: Get a household fan and direct it onto the back of your MacBook Pro which is not a solution but may help.
I am using an iMac and a desktop PC to develop games and I find, especially in a hot climate, that Macs heat up when running demanding software or rendering. My old iMac actually caught fire internally and smoke poured out a few years back whilst outputting video in Final Cut Pro - I was understandably upset at this as it could have easily burned my house down had I not been there. I had to buy a new one after that. Now (as I'm typing this reply even) I have put a stand up fan blowing onto the back of my Mac to cool it down.
Don't get me wrong, I love working on Macs. I worked in graphic design for 13 years on iMacs and they are just so solid and nice to work on, even the Royal Mint in England uses only Macs because they are so stable. However, the thin 'designer look' to Macs comes at a price - the price of less internal space to provide cooling or extra cooling options.
As an example, my PC does not need a fan blowing on it to cool down, the tower has ample space for stronger internal fans and I can customise it quite easily to include extra PC fans if I choose. In contrast my Mac is a real pain to customise.
After my iMac caught fire I decided to transition to a PC, but I still have my newest iMac, albeit the last iMac that I will buy; it is a joy to work on and seems so solid in comparison to Windows / PCs. However, due to the fact that my PC, which was half the price, is slightly more powerful processing wise, is easier to customise, cheaper to fix - plus I can even build my own in the future to the specs I need, such as including extra fans / cooling options . . . I'm sticking with Windows PCs from now on.
Don't get me wrong here, I don't hate Macs as I love Macs for design work and still use my iMac a lot. If I didn't need heavy processing work, rendering, or demanding software I'd be quite happy sticking with Macs - they are just not cut out to be used in hot environments when using demanding software with their wafer thin designs . . . just in my opinion . . . I don't want to offend any fellow Mac users - just the result of my experiences here.
[For Mac users in cold / temperate climates or if you just use social media or surf the internet in Starbucks, you don't have to worry so much and will probably never even come across an overheating problem.]
Personally I think it’s GM. I’ve used other engines and had several programs running and never noticed the fan. I didn’t know I had a fan until I started GM. I can’t say the fan runs more with 2.3. ??????