A faulty vacuum valve in the radiator cap would manifest as which symptom?

• A. Engine overheating.
• B. Collapsed radiator hose.
• C. Extended warm up time.
• D. Overfilled coolant reservoir.

Answer: (B)

The radiator cap’s vacuum valve is there to manage negative pressure as the coolant cools and contracts. When the system is hot, pressure is kept up to raise the boiling point; as it cools, the vacuum valve opens to pull air back in from the expansion reservoir, preventing the hoses from being sucked inward by a strong vacuum. If that valve is faulty and can’t open properly, a vacuum forms and the suction can cause the radiator hose to collapse. A collapsed hose directly signals this vacuum problem and can also restrict coolant flow, risking overheating if it continues. The other options don’t fit as well: extended warm-up time isn’t tied to the valve’s vacuum function, an overfilled reservoir isn’t the symptom of a faulty vacuum valve, and engine overheating isn’t the immediate visual sign of a vacuum valve failure like a collapsed hose is.