What is the difference between a car's upper and lower radiator hoses?
The difference between the upper and lower radiator hoses is where on the engine they are used. They are made of the same material (EPDM), so they both meet the requirements of thermal stability, pressurization, and life expectancy.
The upper hose is primarily a pressure hose. It connects the engine to the radiator so that hot coolant may exit the engine and enter the radiator where it is cooled by ambient air flowing through the radiator. The engine coolant flows to the bottom of the radiator where the cooled coolant gets drawn back into the engine.
The lower radiator hose is primarily a suction hose. The water pump, as it spins, draws coolant from the radiator into the engine. This creates an area of low pressure at the bottom of the radiator, which can cause an ordinary hose to collapse. That is why the lower radiator hose has a wound wire spring on the inside of the hose; to prevent the hose from collapsing. The wire does not extend through the entire length of the hose, however. It is located at the end of the hose that is nearest the water pump.
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