WARNING: This page is about a different car, the 2004 Nissan Maxima. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Exploded View Of Radiator & Components
Courtesy of NISSAN MOTOR CO., U.S.A.
WARNING:
Never remove the radiator cap when the engine is hot. Serious burns could occur from high pressure coolant escaping from the radiator.