Why a laptop slows down when it overheats
The processor has a maximum temperature set. When it gets close to it, it lowers its own performance to avoid being damaged — this is called thermal throttling. That is why overheating shows up not only as heat and noise, but above all as the laptop becoming slow.
It is a protection, not a fault. But it is a signal that the cooling cannot keep up.
Cause 1: clogged cooling
By far the most common cause. A laptop draws in air together with dust, which gradually settles on the heatsink. After two or three years the heatsink is often so clogged that air practically cannot pass through it.
Blowing compressed air in from the outside is usually not enough — the dust is pressed between the fins of the heatsink and has to be removed. When cleaning, we take the laptop apart, clean the heatsink mechanically and also check the fan.
Cause 2: dried-out thermal paste
Between the processor and the heatsink there is a layer of thermal paste that transfers the heat. After three to five years it dries out and loses its effectiveness. Then even a perfectly clean heatsink cannot carry the heat away.
That is why we always replace the paste during a cooling service — cleaning alone without replacing the paste solves only half of the problem.
Cause 3: faulty fan
The fan bearing wears out. This shows up as a characteristic squealing or rattling, or as the fan occasionally stopping completely so that the laptop overheats immediately. In that case the fan is replaced.
What you can check at home
- Put the laptop on a hard surface. On a bed or a blanket the intake vents on the underside get blocked. This alone can make a big difference.
- Check what is running in the background. In the Task Manager (Ctrl + Shift + Esc), see whether something is using tens of percent of the processor for a long time.
- Look at the air exhaust. If only weak hot air comes out of the side vent, the cooling is almost certainly clogged.
Do not blow compressed air into the fan so that it spins. Spinning it above its operating speed damages the bearing and turns a working fan into a noisy one.
How often to clean the cooling
For normal use at home, once every two to three years is enough. In a dusty environment, in a workshop or in a home with pets, rather once a year. For gaming laptops, which are under heavy load for long periods, also about once a year.
It is preventive maintenance that costs a fraction of what a repair after thermal damage to the motherboard would.
More on the page laptop repair, and for Apple devices MacBook repair.