Abstract: A mobile pumping unit including a housing enclosing an engine driven pump. The housing defines an air inlet chamber substantially isolated from an engine compartment. Air drawn into the inlet chamber by an engine driven blower is conveyed along a flow path and absorbs waste heat from the engine and is discharged to the ambient from an exit chamber. The inlet and exit chambers each include acoustic material for controlling noise in the air flow path. A conventional exhaust silencer is disposed in the exit chamber so that noise radiated from its surfaces is also controlled. A ventilation flow path for the engine compartment is established by bleeding off a portion of said cooling air and discharging it through a secondary outlet formed in the housing. A hot air outlet for the cooling air is formed by a self-opening door hingedly mounted to the housing which is automatically opened by the air pressure in the exit chamber when the pump unit is started. The door is operatively connected to an exhaust pipe cover.