Upper and lower radiator hoses, along with the heater hoses, should be checked for deterioration, leaks and loose hose clamps at least every 30,000 miles (48,000 km). It is also wise to check the hoses periodically in early spring and at the beginning of the fall or winter when you are performing other maintenance. A quick visual inspection could discover a weakened hose which might have left you stranded if it had remained unrepaired.
Whenever you are checking the hoses, make sure the engine and cooling system are cold. Visually inspect for cracking, rotting or collapsed hoses, and replace as necessary. Run your hand along the length of the hose. If a weak or swollen spot is noted when squeezing the hose wall, the hose should be replaced.
Worn hoses will feel brittle, the lower hose may be permanently narrowed at one point from suction, or may appear frayed or cracked. New hoses will be springy and pliable yet firm, the rubber surface will be solid and smooth, and there will be no evidence of string reinforcements showing through.