Electric fan assemblies fail at the motor, at the resistor or relay that controls speed, or at the connector that corrodes.
Fan assemblies are listed as fan only, motor only, or complete assembly with shroud. The complete assembly is the usual choice when the shroud is cracked, because a shroud that does not seal lets the fan pull air from around the radiator instead of through it.
Two-speed fans use a resistor pack or a control module. If the fan works on high but not on low, the motor is fine and the resistor is the fault.
Mechanical fans with a viscous clutch fail by freewheeling or by seizing. A seized clutch roars constantly; a failed clutch lets the engine run hot in traffic and cool on the highway.
