OVERVIEW
Genuine O-ring for the specified coolant pipe union
N-900-351-03 is the Genuine VW/Audi O-ring used to seal the original coolant pipe union on the applications below. The nominal factory specification is 21×3.
The seal closes the assigned pipe connection while the surrounding hardware retains the fitting. Cooling systems contain many O-rings of similar appearance, so match the complete factory number and original connection before ordering.
Technical details
- Complete factory number: N-900-351-03.
- Factory specification: 21 mm nominal inside diameter × 3 mm cross-section.
- Design: round-section coolant pipe O-ring.
- Quantity supplied: one individual O-ring.
The bore and cross-section are functional component dimensions. They do not make this seal a universal replacement for another cooling-system joint. Material composition and packaged shipping dimensions are not specified here.
Common reasons to replace
- Coolant seepage is traced to this sealed connection.
- The original ring is flattened or has lost elasticity.
- The ring is cut, cracked or pinched.
- The fitting has been removed for service.
- An incorrect seal was installed during a previous repair.
Inspect the pipe union, receiving bore and sealing surfaces for corrosion, cracking or damage. A new O-ring cannot correct a cracked fitting or damaged sealing surface. Identify the source of a leak before replacing parts.
Vehicle fitment
Use only at the original coolant pipe union assigned N90035103. This seal is separate from the coolant pump perimeter seal and other O-rings in the same system.
| Vehicle | Model years | Engine | Configuration | Application restrictions |
|---|---|---|---|---|
| Audi 4000 quattro | 1985 | 2.2L gasoline I5 | Sedan; quattro; Original coolant pipe union seal | Original coolant pipe union assigned N90035103, nominal 21×3. Confirm the actual connection. |
| Audi Coupe GT | 1984 | 2.2L gasoline I5 | Coupe; Original coolant pipe union seal | Original coolant pipe union assigned N90035103, nominal 21×3. Confirm the actual connection. |
| Audi quattro | 1983, 1985 | 2.1L turbocharged gasoline I5 | Original quattro coupe; Original coolant pipe union seal | Original coolant pipe union assigned N90035103, nominal 21×3. Confirm the actual connection. |
Installation guidance
Allow the cooling system to cool completely and follow the factory draining and depressurizing procedure. Clean the sealing surfaces without damaging them, fit the correct seal without twisting it and use only the installation lubricant specified for the connection.
Refill and bleed the cooling system according to the vehicle-specific procedure, then check the serviced joint for leaks and verify the coolant level after the required cooling cycle.
Ordering information
One genuine O-ring is supplied. The pipe union, retaining hardware, hoses and coolant are not included. Confirm the original number and quantity needed.