The present invention describes an opening for engine compartment cooling. The opening includes a one-way valve that permits airflow only at speed. The valve allows cooling air to circulate past the engine without impeding the efficiency of the radiator. The size, shape and number of openings and valves may vary depending on cooling capacity or styling considerations. The opening includes a leading edge followed by an indentation defining a port for a one-way valve. A valve is fixed in the port so that airflow can occur only in one direction.