Being an owner & user of the 15" MacBook Pro forever; Over the years the 15" has frequently struggled with it`s thermals, especially when an external display is connected as the dGPU switches on as default, internal temperatures soar;
- Elevate the rear, aluminium passive coolers generally work best (I use RainDesign`s mStand & iLap)
- Increase base fan RPM to 3K or as much as you are comfortable with (MacsFanControl or SMC Fan Control)
- Limit the dGPU`s usage with gfxCardStatus
- Swap out Chrome for Chrome Canary as it`s way more optimised for OS X and will extend battery run time, reduce thermals
- Swap out VLC for Movist as again it`s a reduced load on CPU/GPU
- Uninstall or block Flash
- Install an ad blocker Ublock extension works well
- Powered coolers are very much a "mixed bag" when it comes to Mac portables, you need one that has a high capacity (100 CFM minimum) and preferably a large single fan, this can help to keep the 15" internal fans below 4K which for many is good enough as often it`s this point and beyond where the fans become intrusive. Don't expect a powered cooler impact internal temperatures, beyond a couple of degrees
- Older machines can benefit from cleaning of the cooling system
- Replacing the thermal paste has been hit & miss, some with very positive results, some with no improvement over stock. Personally I would only do this on a Mac Portable that was either very old, or one that I can confirm was definitely running hotter than stock.
- If your MBP has a discrete GPU, it will fire up when an external display is connected as default, temperatures will rise rapidly.
The key to a quiet life with a 15" MacBook Pro is several incremental changes that do add up to reduce thermals. From my experience over the years if your going to push a 15" hard the fans are going to max out fast, with associated noise. If your using it with a moderate load life can be made quieter
For the most part your MBP runs hot as that`s how Apple designed it, the trade off for form over, function, thin & light...
Gaming is always going to push your Mac`s internal temperatures way up, nor is the 15" rMBP specifically designed for gaming. The old adage still applies; it`s easier to keep a system cool, than cool-down an already overly hot machine. This being said it`s not strictly necessary, equally it`s nice to know that there are options for reducing temperature out there.
For use on the lap try
iLap by Rain Design, don't expect miracles.
Q-6