Automotive radiator cap

A radiator cap sit on a filler neck of an automotive radiator tank. The radiator cap has an inner cap rotatably connected with an outer cap, a pressure valve functionally connected with the inner cap in such a manner that the pressure valve can move vertically so that the pressure valve opens the filler neck when the pressure within the radiator tank increases up to a predetermined pressure. The radiator cap further includes a coil spring provided between the inner cap and the pressure valve for biasing the pressure valve toward the filler neck. Since the connecting point between the coil spring and the pressure valve locates lower side than the connecting point between a sealing portion of the pressure valve and the filler neck, the rotating moment which returns the pressure valve horizontally is generated when the pressure valve is inclined. So that the pressure valve is well prevented to incline. The pressure valve of the present invention can maintain its position horizontally and can open the filler neck always at the predetermined pressure.