025-121-321B VW Vanagon Coolant Pressure Cap - Blue

Coolant Expansion Tank Pressure Cap (Blue) – 025-121-321B

The 025-121-321B is the upgraded "Blue" pressure cap for the Volkswagen Vanagon's primary coolant expansion tank. This cap is far more than a simple lid; it is a precisely calibrated pressure relief valve. In the Wasserboxer cooling system, maintaining the correct pressure is critical to raising the boiling point of the coolant. The blue cap is the industry-standard replacement for the older, less reliable black caps, as it features an improved internal spring and seal design to regulate pressure more accurately.

A failing cap can lead to two major issues: if it fails to hold pressure, your coolant will boil at a lower temperature, leading to overheating; if it fails to vent, excessive pressure can cause hoses or the plastic expansion tank to burst. Replacing your cap with the 025-121-321B is one of the most cost-effective ways to ensure your Vanagon's cooling system remains stable under the high thermal loads of highway driving.

Detailed Vehicle Compatibility

Fits 1.9L and 2.1L Wasserboxer engines.

VW Vanagon:

• 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991

Product Highlights & Features

• Calibrated Pressure Relief: Designed to hold pressure up to approximately 1.0 bar (14.5 PSI) before venting, protecting your radiator and hoses.

• Upgraded Design: Features a superior internal valve mechanism compared to the original factory black caps, providing better vacuum recovery from the refill tank.

• Durable Sealing: Equipped with a high-quality rubber O-ring that resists heat and chemical degradation from modern antifreeze.

• Essential Safety Component: Acts as a safety valve for the entire cooling system, preventing catastrophic pressure spikes.

Technical Specifications

• Part Number: 025-121-321B

• Color: Blue (Indicates updated internal valve)

• Pressure Rating: 1.0 Bar / 14.5 PSI

• Application: Pressurized Expansion Tank (Main Reservoir)

Installation & Maintenance Tips

• Hand Tighten Only: Do not use tools to tighten the cap. Hand-tightening is sufficient to seat the O-ring; over-tightening can crack the plastic threads on the expansion tank.

• Inspect Tank Threads: Before installing the new cap, ensure the threads on the expansion tank are clean and free of cracks. A new cap cannot seal a damaged tank.

• Coolant Recovery Check: If you notice your "behind the license plate" refill tank is overflowing or not being pulled back into the main system, the pressure cap is often the culprit.

• Never Open Hot: Never attempt to remove this cap while the engine is hot. The system is under high pressure and can spray boiling coolant, causing severe injury.

1114800100

121045004

025121321B