An apparatus and method for cooling an exhaust gas flow of an internal combustion engine of a truck or other vehicle includes a conduit connected to an air source, for example, a turbo driven compressor to deliver air to the exhaust stack or tail pipe. The conduit is controlled by a valve, which is opened and closed by a controller responsive to a measured exhaust gas temperature above a threshold and a vehicle speed below a threshold. The invention is particularly advantageous for engine exhausts having aftertreatment devices that require high temperature regeneration.