Mac fan running loud and stuck at max (thermal throttling)

After this, fan noise tracks actual load again and exports/builds hold their clock speed for the full run.

Why this happens

Apple Silicon chips manage their own thermal ceiling directly: when die temperature approaches the limit, the scheduler lowers the maximum clock speed available to work, and fans (on machines that have them) ramp to compensate. This is the same underlying mechanism behind kernel_task showing very high CPU usage — kernel_task is the process-table symptom, a capped clock speed is the performance symptom, and they show up together. There's no manual SMC reset on Apple Silicon the way there was on Intel Macs — a full shutdown and a fresh power-on already resets that state, so skip any guide that tells you to hold a key combination for it.

The gap between a fanless MacBook Air and a fan-equipped Pro under the same load is real and measurable, not just a spec-sheet difference: one independently-run 30-minute Cinebench R23 loop test posted to MacRumors forums found an M1 Air's score dropping about 10% over 16 consecutive runs, and an M2 Air dropping closer to 15% over 19 runs, with measured core temperatures around 95–105°C by the end of the run. Fan-equipped models in the same test held their scores essentially flat across the full 30 minutes. That's one forum poster's own test rather than a published lab benchmark, but it matches what most Air owners report: the fanless chassis is the limiting factor long before the chip itself would otherwise throttle.

Fix it

1. Confirm the machine is actually thermally limited, rather than just being loud:

   ● Reads the system

   What it does: prints the current thermal and CPU speed/scheduler limits.

   After: nothing changes, this only reads.

   pmset -g therm

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   Output

   Note: No thermal warning level has been recorded
   Note: No performance warning level has been recorded
   Note: No CPU power status has been recorded

   That's the clean baseline from the verification machine at idle. This command is a yes/no on Apple Silicon, not a percentage — the numeric CPU_Speed_Limit field some older guides mention is an Intel-only reading and won't appear here at all.

   For an actual graded reading, sample the thermal pressure level directly — this is the same signal apps get from the public NSProcessInfo.thermalState API, one of five internal levels: Nominal, Moderate, Heavy, Trapping, or Sleeping.

   ● Reads the system

   What it does: samples the current thermal pressure level once.

   After: nothing changes, this only reads. Asks for your password since it needs root to read SMC sensors.

   sudo powermetrics --samplers thermal -i1000 -n1

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   Anything past Moderate mid-workload confirms the throttle is real, independent of fan noise or how the case feels to the touch.

2. If the limit is confirmed and the workload can wait, dropping into low power mode reduces the sustained heat load directly, which is usually enough to stop the throttle from re-triggering every few minutes:

   ▲ Changes settings

   What it does: enables Low Power Mode for all power sources.

   After: sustained CPU/GPU clocks drop, takes effect immediately.

   sudo pmset -a lowpowermode 1

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   Revert: sudo pmset -a lowpowermode 0

3. Check airflow itself: a laptop running on a bed, cushion, or another soft surface blocks the intake vents on the underside, which throttles the machine at a much lower workload than it's rated for. Elevate it onto a hard, flat surface and re-run the workload before assuming it's a hardware fault.

Still broken?

• kernel_task is using huge amounts of CPU by itself
• The Mac won't sleep because something is holding a power assertion — a process holding the machine awake under load is a common co-cause.

When to take it to a shop

If throttling triggers within a minute or two of light, ordinary use — a few browser tabs, no export or compile running — with the machine on a hard surface, that's not workload-driven. Run Apple Diagnostics (hold the power button at startup until options appear, then choose it); a fan or sensor fault will usually be named directly.

Verified on

Related problems

• kernel_task pegging the CPU on its own
• Mac won't go to sleep even with the lid closed
• WindowServer itself is the process using high CPU, not kernel_task