Re: Spring in radiator hose?
When the engine warms up, the coolant will expand and after a certain overpressure the radiator cap pressure relief valve opens internally and lets the coolant flow to the expansion reservoir. When the engine cools down, the coolant will return to its normal volume and an underpressure is created in the cooling system. At a certain underpressure an other valve in the radiator cap opens and coolant from the expansion reservoir returns into the system. The slight underpressure which is created could make the hose colapse and would prevent coolant to return to the cooling system. For that reason they put the spring in the hose, to prevent it from colapsing.