Answer: Heater hoses are made of thick, durable rubber in order to withstand the hot engine coolant passing through them. However, over time, heater hoses will get hard and brittle and can crack. When heater hoses wear and crack, they will leak engine coolant. Heater hoses are actually one of the most common sources of engine coolant leakage. If your heater hoses are leaking engine coolant, not only will your heating system not heat your vehicle as well, but also your cooling system won’t have enough engine coolant and your engine can overheat.