These 1990-1996 Nissan 300zx OEM Heater Core Hoses are located at the back of the engine near the left side firewall. These hose allow coolant to flow through the heater core, and return back into the cooling system. Over the years, they will get brittle and crack. We recommend replacing them every 120K miles or anytime the motor is removed.
Upgraded Silicone hoses can be found here: Silicone Heater Core Hoses