This paper presents on the development of an electronically controlled viscous cooling fan clutch actuator. Improvement in energy efficiency has been achieved by automation of the engine control system and enhancement of engine cooling systems. The engine cooling system uses On/Off viscous cooling fans that are applicable to wide range of engine loads with efficient energy consumptions. Depending on the temperature of the engine and the PWM signals, the power input and speed of the cooling fan automatically controlled by engine management system (EMS). Test results on the fan speed control according to the engine temperature are given in this paper.