NISSAN 21430-D999C Radiator Pressure Cap 118 kPa

The genuine Nissan 21430-D999C radiator pressure cap (CAP ASSY-PRESSU) is a precision pressure-regulating component that plays a vital role in the optimal operation and safety of the vehicle's engine cooling system.

Technical Features and Specifications:

• Rated Pressure Limit: 118 kPa (approx. 1.18 bar), which raises the boiling point of the coolant, preventing engine overheating even under extreme loads.
• Design & Construction: Two-way spring-loaded valve mechanism (pressure relief valve and vacuum return valve).
• Material Quality: Corrosion-resistant metal alloy body with high-temperature and chemical-resistant specialized elastomer (rubber) seals for leak-free performance.
• Manufacturer: Nissan (Genuine OEM part).

Operating Principle and Importance:

The radiator cap does not merely seal the cooling system; it actively regulates internal operating pressure. As the engine warms up, the expanding coolant increases pressure. When pressure reaches 118 kPa, the cap's spring valve opens and vents excess fluid into the expansion tank. As the engine cools down, a vacuum is formed within the system; the integrated vacuum valve opens to allow fluid to return to the radiator, preventing the radiator hoses and radiator core from collapsing or deforming.

Typical Symptoms of Failure:

• Engine Overheating: If the cap fails to hold the specified 118 kPa pressure, the coolant boils at a lower temperature, drastically reducing cooling efficiency.
• Coolant Leakage: Cracked or degraded seals can cause coolant to seep directly past the cap.
• Collapsed Radiator Hoses: If the vacuum valve sticks shut, vacuum created during cooling collapses the rubber hoses.
• Frequent Coolant Loss: Premature opening of the pressure valve can cause unwarranted overflow into the expansion tank.