VW heater hose. This hose passes through the firewall and feeds the coolant to the heater core from the cylinder head. You may find you need to replace the heater hose when you remove the heater core from your Golf, Jetta, or Passat; or it just happened to spring a leak on you. Sold each, 1 required per car.
The heater core that this VW heater hoses connects to is shown below. When you remove the hose from your car inspect the plastic connection point that passes through the firewall. You don’t want this section to be cracked and leaking to your interior. You are going to lose some coolant when you replace the heater hose. Make sure you top off your Jetta, Golf, or Passat with Volkswagen approved German Pentosin coolant.