Old thread, but seems to be the thread with most information about the dreaded kernel_task issue. I have been working with a 2010 MacBook 15" in High Sierra (which is the highest supported OS), updated with a SSD drive, and using an external monitor. I have tried all the other tips here (removing the relevant plist in ACPI_SMC_PlatformPlugin.kext, removing unneeded extra kexts files, and disabling "automatic graphics switching"), but with limited effect. But three additional hacks made all of the difference for me: Disabling Turbo Boost by using the utility "Turbo Boost Switcher Pro". With this, you can turn off Turbo Boost automatically when the fan speed is high. In my Chrome-based browser (I am using Brave, but I suspect it will work in other Chrome-based browsers also): Preferences -> Additional settings -> System -> Disable "Use hardware acceleration when available" (and restart browser) Raising my macbook a bit from the desk using a couple of pencils. Now my 10 year old Mac is running smoothly again!