you cant maintain it ,its like a clutch that allows engine to drive fan but the amount of air it moves depends on temperature of air hitting viscous unit ,when cold little drive will go to fan and you could stop it turning by putting something in it like rolled up news paper in between blades,when hot its locked up and you couldnt stop it ,they are used in place of fixed drive fan as are more economic as power from engine is only used when needed ,yours sounds seized up ,when viscous locks when hot they you can hear them shifting air , see if it turns with engine switched off if seized it wont turn and needs replacing
