You can get a thermostatically controlled viscous fan, they spin along using a viscous drive ,when the air flow through the rad gets hotter a thermostatically controlled valve allows more viscous liquid into clutch drive and the fan drives faster. As the air flow cools down the valve opens and declutches the fan . Kind of works like a torque converter drive.it does this automatically no electric controls. I had this kind of fan in my ford pickup.
