A gas turbine engine comprising: a compressor section, a combustor, and a turbine section; a bleed tap for tapping air from said compressor section through a bleed valve, the bleed valve selectively opened by a control to dump air from the compressor section to a dump outlet, wherein said control is programmed to open said bleed air valve when the gas turbine engine is operating at at least one of an idle condition, or when said gas turbine engine is accelerating at lower power or decelerating at high power; a heat exchanger duct including a duct air inlet to cool a fluid in a heat exchanger and a duct air outlet, and said dump outlet being within said heat exchanger duct; and a fan positioned to selectively deliver air to said compressor, and also to deliver air into a bypass duct, wherein said duct air inlet takes air from said bypass duct, and said duct air outlet delivers air mixed from said duct air inlet and from said dump outlet back into said bypass duct; wherein said dump outlet is downstream of a downstream end of said heat exchanger, said dump outlet is at a radially outer position within said heat exchanger duct, said dump outlet includes a plurality of orifices or an elongated slot and sits inward of the radially outer wall of the downstream section of said heat exchanger duct said heat exchanger duct has a downstream end provided with structure to withstand relatively high temperatures, and said dump outlet directs air in a direction with a component which is radially outward relative to a rotational axis of the engine such that the air is directed radially outwardly of an inner wall of the bypass duct. a compressor section, a combustor, and a turbine section; a bleed tap for tapping air from said compressor section through a bleed valve, the bleed valve selectively opened by a control to dump air from the compressor section to a dump outlet, wherein said control is programmed to open said bleed air valve when the gas turbine engine is operating at at least one of an idle condition, or when said gas turbine engine is accelerating at lower power or decelerating at high power; a heat exchanger duct including a duct air inlet to cool a fluid in a heat exchanger and a duct air outlet, and said dump outlet being within said heat exchanger duct; and a fan positioned to selectively deliver air to said compressor, and also to deliver air into a bypass duct, wherein said duct air inlet takes air from said bypass duct, and said duct air outlet delivers air mixed from said duct air inlet and from said dump outlet back into said bypass duct; wherein said dump outlet is downstream of a downstream end of said heat exchanger, said dump outlet is at a radially outer position within said heat exchanger duct, said dump outlet includes a plurality of orifices or an elongated slot and sits inward of the radially outer wall of the downstream section of said heat exchanger duct said heat exchanger duct has a downstream end provided with structure to withstand relatively high temperatures, and said dump outlet directs air in a direction with a component which is radially outward relative to a rotational axis of the engine such that the air is directed radially outwardly of an inner wall of the bypass duct.