After many years of successful Visco fan drive applications, Behr has now transferred the Visco technology to the coolant pump drive. The continuously variable Visco drive allows the coolant pump to deliver the optimum flow dependent upon the requirements, therefore reducing the drive power to the minimum possible.Up to now coolant pumps, world wide, have almost always been powered by direct, uncontrolled drives. Consequently, the delivery and the power consumption have been directly related to the engine speed, which, in many conditions, results in an unnecessarily high flow rate. The potential to reduce the flow rate is inherent within the Visco coolant pump.As a concept with continuous control of the impeller speed it has been found to be more fuel efficient than incremental impeller speed control or concepts which only restrict or divert the flow rate. The torque transmission via the shear forces of a silicone oil results in a robust and wear-free drive unit. The use of a speed sensor allows both a closed loop control system, with the impeller speed following precisely the demands, and a feedback on the reliable operation of the pump. The actuation system has been designed as fail-safe: the loss of electric supply leads to full engagement of the impeller. With the help of a special bearing design the packaging of the drive unit mostly within the space of the pulley could be achieved. After successful validation on component test rigs, on engines and in vehicles the series production of the Visco coolant pump has been launched in 2011.