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

This BLAU-manufactured expansion tank cap is a high-quality German-made 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. Featuring a screw-on design and a correct 1.1 bar pressure rating, it ensures reliable and consistent cooling system pressure control.

BLAU are well known for producing precision-engineered cooling system components, and this cap is manufactured to strict OEM standards. Compared to low-quality aftermarket caps, it offers more accurate pressure regulation and longer service life—critical for protecting Waterboxer engines, which rely heavily on stable cooling system pressure.

The expansion tank cap is responsible for maintaining system pressure as coolant heats and expands. A failing or incorrect cap can allow pressure loss, premature boiling, coolant leaks, or air ingress into the cooling system. Replacing the cap with a quality German-made unit is a simple but essential step in maintaining engine reliability.

How it works

As engine temperature rises, coolant expands and system pressure increases. This BLAU cap regulates pressure up to 1.1 bar, raising the coolant’s boiling point and allowing excess pressure to vent safely. As the system cools, the cap allows coolant to return, maintaining correct coolant levels and preventing air locks.

Fitment & installation notes

• Fits screw-type expansion tanks

• Suitable for petrol and diesel T25 / T3 models

• Correct 1.1 bar pressure rating

• Manufactured by BLAU (Germany)

• Direct screw-on replacement

Additional option:

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

Replacing the expansion tank cap is strongly recommended when servicing the cooling system, renewing coolant, or diagnosing unexplained coolant loss or overheating issues.

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)