The vehicle has a main coolant circuit (2) for the IC engine comprising a pump, radiator (4) and blower. The heating system for the interior of the vehicle has a separate coolant circuit comprising a viscous heat generator, a heat exchanger 912) and a blower (15). The heat is generated by a rotating disc inside a viscous fluid to shear the fluid. The rotating disc is coupled to the IC engine by a belt drive and a solenoid clutch (30). The rotating disc is on a narrow fluid chamber separated from the heater coolant circuit by a wall across which the heat transfer to the coolant. The solenoid clutch is operated as and when heating is required. A controller (37) operates the blower, pump and clutch.
