Actually its a Thermostatic Spring Viscous bearing type. The more the front thermo loaded spring heats up it tightens on the Viscous bearing causing less free run of the bearing , ultimatlly increasing the speed of the fan with the engines revolution , pulling more air thru the radiator , cooling down the coolant. As the air flowing thru the radiator drops in temp and the thermostatic frunt hub and loaded spring retract allowing more free spin of the fan against the viscous bearing. Yu can sorta tell by , with the engine off turn the fan by hand and see how freely it spins , it should have some resistance , also when fully cold , have sumone start the vehicle and observe the fan , at start up yu should hear the fan draw alot of air and then ease up . And as the vehicle warms up in idle in one position yu should audibly hear the fan increase in velocity . Stop the vehicle , if the fan spins a bit that is a sign that the fan clutch is not working correctlly.
But as mentioned coolant and radiator flushes are a very important thing to get done. A low flow , by restricted radiator passages in the radiator can cause cooling issues.