Factors to Heat Dissipation
There are 3 basics to heat dissipation. Moving the heat away from the heat source, expanding the surface area and airflow. A bad radiator cooling fan won’t provide the adequate airflow.
The role of the fan is to move air through the radiator. But pushing air through a restriction is energy intensive.
Air much like water requires quite a bit of energy to move. A weak fan will spin but the force it exerts won’t move a significant volume of air.
There are 2 styles of fans, one is linked to engine rpm, while the other is driven by an electric motor.
The one linked to engine rpm has a clutch in it to decouple the fan at higher rpm. As it can disengage, it also has to lock back on. The fan clutch is a wear item, overtime it will lose the ability to grip. To supplement airflow, it is frequent to see an electric auxiliary fan. Using a custom fan controller to increase airflow provided by the auxiliary fan can compensate for a weak fan clutch.
If the fan is electrically controlled, either the fan itself could be failing and spinning slower than required or the control module could be on its way out and not providing enough power. These are complex modules that monitor the actual speed of the fan and can adjust power levels to meet the target.