Q: What are the symptoms of a bad radiator cap?
A: A radiator cap has several functions. (1) It keeps the cooling system sealed from outside contaminants. (2) By keeping pressure on the cooling system, it raises the boiling point. (3) The radiator cap allows coolant to go to the expansion recovery tank when coolant gets hot, expands, and pressures increase. (4) As the system cools down, it allows coolant to return to the engine from the expansion recovery tank. A bad radiator cap can cause the engine to overheat at lower temperatures. This will cause the coolant to boil over to the expansion tank. A radiator cap that is faulty could also prevent coolant from returning to the engine. This would create a vacuum and cause the radiator hoses to collapse.