A self-contained portable unit for steam generation and injection by means of an injector wellhead hanger of coiled jacketed capillary tubing with a closed circuit and procedure for operation in oil wells comprises a portable, self-contained equipment for injection and dewaxing of heated fluids mounted on a hauler that includes a heat exchanger, a water tank, a heat exchanger, a softener, a centrifugal pum, a lubricant tank, a power engine, an electrical power generator, a control cabin, a fluids softener, a steam boiler, a reservoir tank, a fuel tank, a hose reel and one hose set for two lines of fluid injection and return of that connect to a wellhead hanger/injector for two capillaries making up a closed circuit. This wellhead includes three module and crowned with a lid, two of which are hangers and the rest are injection-type.