Excessive coolant system pressure can be caused by a defective

• A. Radiator cap
• B. Thermostat
• C. Water pump
• D. Cylinder head gasket

Answer: (D)

Excessive coolant system pressure is most often caused by a breach between the engine and cooling system, such as a defective cylinder head gasket. When the head gasket fails, high‑pressure combustion gases can leak into the coolant passages, pressurizing the entire cooling loop beyond what the system relief can handle. This pushes coolant out and can lead to overheating. A radiator cap, while it regulates pressure, doesn’t create that extra pressure by itself; a faulty thermostat or water pump changes flow and temperature rather than directly raising the system pressure. So the head gasket is the root issue that directly raises coolant pressure.