A method for controlling a cooling system for a vehicle having an internal combustion engine permits rapid warm-up of the engine by the use of two electrically-operated valves in addition to a conventional thermostat. The method includes controlling a bypass valve and a heater valve to both remain closed at low coolant temperatures and engine speed to inhibit coolant flow through the engine. A control unit opens the bypass valve to prevent cavitation in the water pump if engine speed and/or load exceeds a certain value. The heater valve is opened when a threshold engine coolant temperature is reached permitting warming of the heater matrix.