A device to reduce the visible and infrared signature of a military combat vehicle by diluting the engine's exhaust and cooling gases. The device includes a caisson receiving both sources of heat flow to ensure a single outlet for both the exhaust gases and the cooling air. The caisson is constituted by an enclosure and a shutter. The enclosure ensures a homogeneous mixture of the two fluids and the shuttering provides a way by which the mixture is evacuated. The air outlet of the dilution device may be positioned between the axles of a wheeled-type vehicle.