The radiator hose transfers coolant from an engine's water pump to the radiator. An upper hose connects the top of the radiator to the top of the engine. A lower hose connects the bottom of the radiator to the water pump, which keeps coolant flowing through the system. It’s a good idea to replace the hoses every five years or 40,000 miles. If you see a crack or bulge in the radiator hose, you should have it replaced immediately. New radiator hoses are an inexpensive repair and can prevent future damage. A leaking radiator hose will not let the engine get the proper amount of coolant. If ignored long enough, the engine will overheat, causing substantial damage. From a safety standpoint there is a slight risk, because an overheated engine might leave you stranded. From an environmental point of view, there is a significant impact, because leaking coolant can be dangerous to children, pets and animals.