This is a very common arrangement found on many Corvettes up to the C4 models. It's a viscous or "clutch" fan. This is the fan type that, in most cases, should deliver the best performance in any vintage Corvette. Yes, it's an OEM factory clutch fan. And it's certainly not a trick, sophisticated piece. In operation, the clutch allows the fan to speed up or slow down-again dependent upon engine or pulley speed. Because of this, the fan decouples as engine speed increases, more or less freewheeling at high rpm. Given the freewheeling nature, there's little power loss when the car is accelerating. In contrast, the fan couples up when the engine speed is low. By coincidence (or perhaps more correctly, design) this gives the engine the maximum amount of cooling when it's needed the most.