Heater Hose
Rubber hoses that route hot engine coolant to the cabin's heater core and back to the engine.
Heater hoses are flexible, heat-resistant rubber lines that connect the engine's cooling system to the heater core inside the dashboard. They carry hot coolant to and from the cabin to provide passenger heating and windshield defrosting.
The system uses two hoses: an inlet hose that routes hot coolant from the engine block or water pump to the heater core, and an outlet hose that returns the cooler fluid back to the engine to be reheated. They are made of reinforced rubber to withstand heat and pressure.
Because they are exposed to engine bay heat and vibrations, heater hoses can degrade over time. They can become soft and spongy, swell near connections, or dry rot and crack, leading to coolant leaks under the hood or wet carpets inside the cabin if a leak occurs at the firewall.
Regularly inspecting heater hoses for soft spots and cracks during routine maintenance is recommended. Replacing old hoses before they burst prevents sudden coolant loss and engine overheating.