Type 25 Water Expansion Tank Cap (For Pressurised Tank) - 1984-92

This expansion tank cap is a correct replacement for almost all VW Type 25 / T3 buses from 1984 to 1992, including 1.9 and 2.1 Waterboxer petrol engines and 1.6 / 1.7 diesel models. It features a screw-on design and is pressure rated to 1.1 bar, ensuring proper cooling system operation and pressure regulation.

The expansion tank cap plays a critical role in maintaining the correct pressure within the cooling system. By controlling pressure, it raises the boiling point of the coolant and allows excess pressure to vent safely when required. A worn, weak, or incorrect cap can lead to coolant loss, overheating, or air entering the system—issues that are particularly damaging on Waterboxer engines.

Manufactured to meet original specifications, this cap provides a secure seal on the expansion tank and ensures the cooling system maintains stable pressure during normal driving conditions. It is an essential service item and should always be replaced if there are signs of leakage, pressure loss, or unexplained coolant issues.

How it works

As coolant heats up, pressure builds within the cooling system. This cap regulates that pressure to a maximum of 1.1 bar, releasing excess pressure safely and drawing coolant back into the system as it cools. Correct pressure control is vital for preventing overheating and protecting hoses, seals, and engine components.

Fitment & installation notes

• Fits screw-type expansion tanks

• Suitable for petrol and diesel T25 / T3 models

• Pressure rated to 1.1 bar

• Simple screw-on installation

• If you require a complete expansion tank with cap, see part number 025121403A

Replacing the cap is strongly recommended when renewing coolant, replacing hoses, or diagnosing cooling system pressure problems.

Engine compatibility

Petrol – Waterboxer:

• DF 1.9 (from chassis 24D089113>> 01/84–07/92)

• DG 1.9 (from chassis 24D089113>> 01/84–07/92)

• DH 1.9 (from chassis 24D089113>> 01/84–07/85)

• EY 1.9

• GW 1.9

• SP 1.9

• MV 2.1

• DJ 2.1

• SR 2.1

• SS 2.1

Diesel:

• CS 1.6 diesel (from chassis 24E070001>> 12/83–07/87)

• JX 1.6 turbo diesel (from chassis 24E070001>> 12/83 onwards)

• KY 1.7 diesel (all)