A heat exchanger arrangement for a gas turbine engine. The arrangement including a flow path within an outer cowl, which flow path locates a heat exchanger part way therealong. A valve is provided at an inlet end of the flow path to selectively receive fluid into the flow path from outside of the cowl and/or from a pressurised fluid flow. An exit from the flow path includes a plenum chamber to receive exhausted coolant flows from the heat exchanger and possibly other exhaust flows. The heat exchanger exhaust flow is then utilised to provide cooling to engine structures.