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MacBook overheating, loud fan and sluggish performance

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Quick answer

A loud fan and overheating are almost always caused by one of three things: 1) dust in the fan and vents, 2) dried-out thermal paste after 4–5 years of use, or 3) a macOS process using 100% CPU. Cleaning and a thermal paste swap with us costs DKK 800–1,500 and typically gives the MacBook another 3–5 years of life.

Why is the MacBook fan running at full blast?

MacBook fans are controlled by temperature sensors on the CPU and GPU. As long as the temperature is below a threshold, they run quietly (1,500–2,000 RPM). As the temperature rises, fan speed ramps up.

If the fan is constantly running at full blast (5,000–7,000 RPM), there are three possibilities:

  1. Something is generating too much heat — check Activity Monitor for a process using 100% CPU
  2. The cooling system can’t shed the heat — dust or dried-out thermal paste
  3. A sensor fault on the logic board — a temperature or power sensor that’s failing

Diagnosis: software or hardware?

Test 1: listen at idle. Close all apps. Let the MacBook sit for 5 minutes. If the fan is still running loudly, it’s hardware (dust or thermal paste). If it quiets down, it’s software load.

Test 2: check Activity Monitor. Cmd+Space → “Activity Monitor”. Sort by %CPU. The classic culprits:

  • mds / mds_stores — Spotlight indexing (wait a few hours, it finishes itself)
  • photoanalysisd — Photos analysing faces (only runs while the MacBook is on the charger)
  • kernel_task — if this is using around 100% (or more), that’s thermal throttling, not a process you can “kill”
  • Browser tabs (Chrome is the worst) — close them and try again

Test 3: boot into Safe Mode. If the problem disappears in Safe Mode, it’s a kernel extension or startup app causing trouble.

What does it cost?

  • Dust cleaning + thermal paste swap: DKK 800-1,500 depending on model
  • Fan replacement (if the bearings are worn): DKK 1,500-2,500
  • Both at the same time: combined price

See the current price for your model at macmo.dk/reparation.

Where can I get it done?

We have a standard “MacBook tune-up” service: opening, removing the old thermal paste, cleaning every heatsink fin and fan, applying premium thermal paste (Arctic MX-6 or equivalent), reassembly, and testing. It typically takes 60–90 minutes.

The result: the fan runs at lower RPM under the same load, CPU temperature typically drops 10–20°C, and the MacBook feels noticeably faster because thermal throttling is gone.

Prevention

  • Use the MacBook on a hard, flat surface — beds and sofas block the vents
  • Clean out dust every 2–3 years, even if nothing seems wrong
  • Replace the thermal paste every 4–5 years alongside a cleaning

How to check whether your MacBook is overheating

⏱ PT3M

  1. Install iStat Menus, Macs Fan Control or Stats. All are free to try and show real-time CPU temperature, fan RPM and throttling status.
  2. Let the MacBook sit idle for 5 minutes. Close all apps. Idle CPU temperature should be 35–50°C on Apple Silicon, 50–70°C on Intel.
  3. Run Geekbench or a 4K YouTube video. Stress the CPU. Check the temperature after 10 minutes.
  4. Read out throttling. If the CPU hits 100°C or the throttling flag activates under normal use, your MacBook isn't healthy. Get in touch with us.
  5. Check fan RPM. If the fan is running above 5,000 RPM at idle, there's a hardware problem. Book a cleaning.

Frequently asked questions

Why is my MacBook fan so loud?
In 70% of cases: dust in the fan and heatsink. When airflow is blocked, the fan has to spin twice as fast to keep the temperature down. With us, a thorough cleaning + thermal paste swap is a standard service at DKK 800-1,500 depending on model. If the fan also needs replacing (worn bearings): DKK 1,500-2,500. See current pricing at macmo.dk/reparation.
How hot is too hot for a MacBook?
CPU temperatures up to 100°C are normal under heavy load (video editing, gaming). But above 100°C, thermal throttling kicks in: the CPU is throttled to a third of its performance to protect itself. If the MacBook is hitting that state during everyday tasks, it's overheating and needs cleaning.
How often should you replace the thermal paste on a MacBook?
Apple doesn't use premium paste, and it typically dries out after 3–5 years. If your MacBook is older than 4 years and quickly gets hot, it's almost always the thermal paste. With us, this is a 60-90 minute job.
My MacBook has suddenly become slow — what could it be?
First check Activity Monitor (Cmd+Space → 'Activity Monitor'). Sort by CPU. If a process is using 100% constantly — especially 'mds', 'mds_stores', 'photoanalysisd', 'kernel_task' — restart or kill the process. If kernel_task keeps using 100%, that's thermal throttling. It's overheating or a sensor fault on the logic board — contact us.
Can I clean the MacBook fan myself?
On older MacBooks with a screwed-on bottom, a careful compressed-air cleaning through the vents can help. But for a thorough cleaning the MacBook has to be opened and the fan removed — that takes precision. We also clean the heatsink and replace the thermal paste in the same visit.