Which feature characterizes a pressurized closed cooling system?

• A. Has a pressure cap on top and operates at pressures above atmospheric
• B. Has a vent on top and operates at atmospheric pressure
• C. Uses open to sea water and operates at ambient pressure
• D. Has no pressure relief and operates under vacuum

Answer: (A)

A pressurized closed cooling system keeps the coolant in a sealed loop and operates above atmospheric pressure. The pressure cap on top sets and regulates that pressure, allowing excess to vent into an expansion reservoir while keeping air out of the coolant. Keeping the system pressurized raises the coolant’s boiling point, so the engine can run hotter without boiling over. This sealed arrangement distinguishes it from open or sea-water cooling, which vent to atmosphere and operate at ambient pressure. The presence of a cap and a maintained pressure above atmospheric are the defining features.