How it works
A heatsink conducts heat away from a component and spreads it over a larger surface. Fins increase the surface available to surrounding air; some coolers add heat pipes and a fan to move energy and air more effectively. The heatsink is one part of the whole cooling path. Heat must first cross the component's contact surface, then leave the cooler through adequate airflow or another designed cooling medium.
Good performance depends on mounting, contact material, unobstructed fins and ventilation. A larger heatsink is not automatically suitable: it must fit the socket, case height and nearby parts, and its mounting hardware must match. A fan spinning does not prove that contact with the processor is correct. Similarly, a processor reaching a high temperature can reflect workload or power settings as well as a cooler problem.
Practical checks
Check the exact cooler and device installation instructions before removing anything. Keep the system powered off and follow supported handling precautions. If the cooler is removed, renew the contact material as the manufacturer directs and mount it without improvising pressure or fasteners. Afterwards, verify fan connection and monitor behaviour during a representative task. Investigate abnormal changes rather than comparing one temperature reading with an unrelated computer's cooler or workload.