Dust and dried paste: the cheapest laptop repair there is
The short answer
Dust packs into the heatsink fins until air cannot pass, and the thermal paste between the chip and the heatsink dries out. The machine throttles itself to avoid overheating, which is why it gets slow and loud before it starts shutting down. A clean and repaste fixes most of it.
Where the heat is supposed to go
The processor produces heat at a small point. A copper plate sits against it, a heat pipe carries the heat to a stack of thin metal fins at the side of the machine, and a fan pushes air through those fins and out the vent.
Between the chip and the copper plate is thermal paste. The two surfaces look flat and are not, at the scale that matters, so the paste fills the microscopic gaps that would otherwise be air. Air is a very poor conductor of heat, which is the entire reason the paste is there.
Two things break that chain over a few years, and both are maintenance rather than failure.
Dust, and dried paste
Dust does not spread evenly through the machine. It gets pulled through the fan and packs into the front face of the fin stack as a felt mat, and once that mat forms almost no air passes. From outside the machine looks clean and the fan is roaring.
Thermal paste dries. It starts as a compliant grease and ends as a chalky layer that has pulled away from the edges of the chip, so heat that used to cross in milliseconds now sits there.
The result is a machine that is fine at idle and unusable under load: loud, hot on the underside, and slow because it is throttling the processor to stop itself overheating. If it gets far enough, it shuts down to protect itself.
- Loud fan at idle, or a fan that never stops
- Hot on the underside, particularly toward the back
- Fast for a minute then slow, which is throttling rather than a failing processor
- Shutting down under load, or during a video call, or while gaming
- Worse in summer, and worse on a bed or a sofa where the vents are blocked
What a clean and repaste involves
- Open it and get the battery disconnectedAlways first.
- Remove the heatsink assemblyWhich means the fan, the heat pipe and the fin stack, as one unit on most machines.
- Clear the fins properlyNot blown through from outside, which packs the mat harder. The stack comes off and the mat comes out.
- Clean the old paste off both surfacesChip and plate, back to bare metal.
- Apply fresh paste and refit at the right pressureToo much paste is as bad as too little, and the screws go down in the order the manufacturer specifies.
- Run it under load and watch the temperaturesWhich is the only way to know it worked.
When it is not dust
A fan that has failed rather than clogged, which sounds like a rattle or nothing at all rather than a roar.
A vent physically blocked, which on a machine used on a duvet is common and free to fix.
Software: one process pinning the processor, which shows up in the activity monitor or task manager in ten seconds and costs nothing to check.
And occasionally a genuine board fault, where something is drawing far more current than it should. That is a diagnostic rather than a clean, and the free one tells the two apart.
Common questions.
Almost always dust packed into the heatsink fins, plus thermal paste that has dried out. The fan runs harder because the air cannot get through. A clean and repaste is one of the cheapest jobs we do.
It helps a little and it often makes the mat in the fins denser rather than removing it. Getting the heatsink off and clearing it properly is what actually works, and it is the only way to also replace the paste.
Every three to five years on a machine in normal use, sooner on one that runs hot or lives in a dusty room. Most laptops never have it done at all, which is why so many arrive here slow and loud.
Usually not. That is thermal protection working, and it means the heat is not getting out. A clean and repaste fixes a large share of these and it is a fraction of the cost of anything else.
No. Check for one process using the whole processor first, in the activity monitor or task manager. That costs nothing and it is a common cause.
Where this leads.
Something actually broken? Bring it in.
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