N-904-520-02 Genuine VW/Audi Coolant Pipe O-Ring

Genuine VW/Audi coolant pipe O-ring, part number N-904-520-02. This original sealing ring closes the assigned water-tube connection at the thermostat housing on the configurations below. It is supplied individually for pipe, thermostat housing or related cooling-system service.

Technical details

• Original number: N-904-520-02 / N90452002.
• Published nominal dimensions: 11 x 3 mm.
• Specified application: thermostat-housing-to-water-tube sealing connection.
• One O-ring supplied. Water tube, thermostat housing, other seals, fasteners and coolant are separate.

The O-ring forms the fluid seal at its assigned pipe connection. Correct dimensions and undamaged mating surfaces allow the tube and housing to assemble with the intended sealing arrangement. The ring does not replace the pipe, housing or separately specified retaining hardware.

A cooling-system assembly can contain several similar-looking rings at different connections. Match N90452002 at the actual water tube before ordering. This small pipe seal is distinct from a larger thermostat perimeter gasket or coolant temperature sensor seal.

Common reasons to replace

Renew the ring when the pipe connection is opened and the applicable service procedure requires a new seal. Replace a ring that is cut, flattened, hardened, swollen or otherwise damaged, or one that no longer seats correctly in its assigned position.

Coolant residue or a diagnosed leak at the water-tube connection can indicate a sealing issue. Inspect the tube, thermostat housing and neighboring coolant components to establish the actual source before selecting repair parts.

Previous installation can pinch or twist a ring, while an incorrect substitute may prevent the pipe from seating normally. Replace unsuitable sealing hardware and inspect the housing contact area before reassembly.

A new ring cannot repair a cracked housing, damaged pipe end, distorted sealing bore or leak from a nearby hose. Correct the diagnosed component fault before completing the connection. Cooling performance complaints also require diagnosis of the wider system.

Installation and service notes

Follow the factory procedure for the exact coolant pipe and thermostat arrangement. Allow the cooling system to cool and release pressure as prescribed before opening the connection. Collect coolant using the required service method.

Remove the old ring carefully and inspect the pipe sealing area and housing bore. Clear old seal material and debris without damaging the contact surfaces. Correct a cracked, corroded or distorted mating component before installing the new seal.

Fit the ring in its prescribed position and use only the installation preparation specified by the procedure. Avoid twisting, cutting or pinching the ring as the pipe enters the housing.

Seat the pipe fully and install the correctly specified retaining hardware. Do not use fastening force to draw an incorrectly aligned pipe into place or to compensate for an unsuitable seal. Check engagement and component positioning before refilling.

Restore the cooling system with the specified coolant and filling or bleeding procedure. The O-ring number does not establish coolant specification, fill quantity or thermostat operating temperature. Select fluid and other service components separately for the vehicle.

Complete the required leakage and operating-temperature checks after assembly. If seepage persists, inspect pipe seating, seal condition and both mating surfaces before continuing operation. This listing supplies one original O-ring rather than a complete thermostat housing seal kit.

Fitment

Confirm original N90452002 at the actual thermostat water-tube connection before ordering. One O-ring supplied.