Excessive pressure entering the coolant system might be caused by a defective

Excessive pressure entering the coolant system might be caused by a defective

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

Answer: (D)

Excessive pressure in the coolant system comes most directly from a defective cylinder head gasket because that gasket keeps the combustion chamber sealed from the cooling passages. When it fails, high-pressure combustion gases can squeeze into the coolant channels, pushing up the pressure inside the radiator and hoses. This gas ingress explains why the system becomes over-pressurized and can lead to coolant loss, foaming, and other related symptoms. The other components play different roles. A radiator cap is a pressure-relief device, and if it fails it can mess with pressure, but it doesn’t introduce gases into the coolant. The water pump mainly affects coolant flow; a bad pump can cause overheating and related pressure rise from heat, not from gas entering the coolant. The thermostat controls flow as well; a stuck-closed thermostat can trap heat and raise pressure indirectly, but again it doesn’t allow combustion gases into the cooling system. So the presence of gases in the coolant due to a breached head gasket best explains excessive coolant-system pressure.

Excessive pressure in the coolant system comes most directly from a defective cylinder head gasket because that gasket keeps the combustion chamber sealed from the cooling passages. When it fails, high-pressure combustion gases can squeeze into the coolant channels, pushing up the pressure inside the radiator and hoses. This gas ingress explains why the system becomes over-pressurized and can lead to coolant loss, foaming, and other related symptoms.

The other components play different roles. A radiator cap is a pressure-relief device, and if it fails it can mess with pressure, but it doesn’t introduce gases into the coolant. The water pump mainly affects coolant flow; a bad pump can cause overheating and related pressure rise from heat, not from gas entering the coolant. The thermostat controls flow as well; a stuck-closed thermostat can trap heat and raise pressure indirectly, but again it doesn’t allow combustion gases into the cooling system. So the presence of gases in the coolant due to a breached head gasket best explains excessive coolant-system pressure.