OVERVIEW
Renew the seal between the original coolant cap and reservoir
1H0-121-687-A is the Genuine VW/Audi sealing ring for the specified coolant expansion-tank caps. Its nominal 28.5 × 3.8 mm dimensions must match the original serviceable cap and sealing arrangement.
The seal helps contain coolant at the cap-to-reservoir connection. The cap's pressure-regulating mechanism and the reservoir neck are separate parts of the system, so replacing the ring alone is appropriate only when those components remain serviceable.
Technical details
- Complete factory number: 1H0-121-687-A.
- Factory specification: nominal 28.5 × 3.8 mm expansion-tank cap sealing ring.
- Design: black circular elastomer seal, as shown in the archive photograph.
- Quantity supplied: one individual cap seal.
One individual sealing ring is supplied. Expansion tank, pressure cap, coolant, hoses and other seals are separate. The nominal ring size is a functional part dimension and is not a packaged shipping measurement.
Common reasons to replace
- The original seal is cracked, flattened or hardened.
- A leak is confirmed at the cap's sealing surface.
- The ring is damaged during approved cap service.
- The original ring is missing from a cap designed to use this service seal.
Inspect the reservoir neck and complete cap. Coolant residue can have several causes, including a damaged tank, an incorrect cap or a pressure-control fault. Diagnose the cooling system and replace a faulty cap assembly when required.
Vehicle fitment
Confirmed cap-seal applications are listed below. Compare the installed cap, seal profile and complete factory number. A cap supersession or an aftermarket cap can use a different sealing arrangement.
| Vehicle | Model years | Engine | Configuration | Application restrictions |
|---|---|---|---|---|
| Volkswagen Cabrio | 1995–2002 | 2.0L gasoline | Convertible; original matching reservoir cap | Assigned cap sealing ring only; confirm the installed cap's serviceable seal design. |
| Volkswagen Passat | 2000–2001 | 1.8L turbocharged gasoline or 2.8L gasoline | Sedan or wagon; original matching reservoir cap | Factory reservoir-cap seal position; verify cap and original number. |
| Volkswagen Golf SportWagen | 2015 | 1.8L turbocharged gasoline or 2.0L TDI | Wagon; original matching reservoir cap | Assigned cap seal; not a hose connector O-ring. |
| Volkswagen GTI | 2024 | 2.0L turbocharged gasoline | S hatchback; original matching reservoir cap | Original cap sealing-ring position; inspect cap and reservoir neck separately. |
Installation guidance
Allow the cooling system to cool completely before following the prescribed pressure-release procedure. Remove the old ring without damaging the cap groove, clean the seat and install the new seal evenly. Use only any lubricant specifically required by the repair procedure.
Check cap installation and perform the required cooling-system leak or pressure test. Verify coolant level and inspect the serviced area after normal temperature cycling.
Ordering information
One individual Genuine VW/Audi 1H0-121-687-A coolant expansion-tank cap seal, nominal 28.5 × 3.8 mm. Cap, reservoir and coolant are sold separately.