1K0 121 407A Coolant Expansion Tank for VOLKSWAGEN

The 1K0 121 407A coolant expansion tank is catalogued for Volkswagen cooling systems that require a translucent reservoir with coolant-level monitoring. It provides a visible reserve volume for thermal expansion while returning coolant to the sealed circuit as temperature falls.

This page is written for parts buyers comparing OE references across Golf, Jetta, GTI and related VAG platforms. Because cap specification, sensor connector and hose routing can vary, the removed reservoir and VIN catalogue remain essential approval evidence.

Product Technical Specifications

Product type: Coolant Expansion Tank

Primary OE reference: 1K0 121 407A

Internal item code: VM01015-003

Vehicle brand: VOLKSWAGEN

Application reference: VW Golf, Jetta, GTI and related 1K-platform applications; confirm by VIN and removed tank.

Cross-reference numbers: 1K0 121 407A

Cooling-Circuit Function and Level Monitoring

During heat cycles, coolant volume changes and pressure must be managed without allowing air to enter the engine circuit. The reservoir supports deaeration, level observation and recovery flow, while the integrated sensor location allows the vehicle to monitor a low-coolant condition.

Identification Before Purchase

Check 1K0 121 407A against the moulded number, electrical plug orientation, lower outlet position and the number of mounting ears. A similar round VAG bottle may look interchangeable in a photograph but use a different sensor, cap or hose layout.

Workshop Replacement Review

Replace a tank that shows seam seepage, heat whitening, stained plastic, a distorted cap neck or cracked hose spigots. After installation, use the coolant specification approved for the vehicle, bleed the circuit correctly and inspect the cap seal and every hose joint as the engine reaches operating temperature.

Quality-Control Focus

Incoming inspection should cover moulding seams, cap threads, sensor pocket, port roundness and tab alignment. The reservoir must remain stable on a flat fixture and the plastic surfaces should be free from flash that could interfere with hoses, clips or electrical connection.

Wholesale Planning for VAG Applications

Distributors can request samples using OE 1K0 121 407A and SKU VM01015-003. Quotation review is faster when the request includes vehicle market, engine or chassis information, annual quantity, cap requirement and preferred neutral or private-label packaging.

Frequently Asked Questions

Is 1K0 121 407A a coolant tank or a steering-oil reservoir?

It is identified as a coolant expansion tank. Its part-number group and level-sensor arrangement belong to the engine cooling circuit, not the hydraulic steering system.

Which Volkswagen models commonly use this reservoir family?

References include Golf, Jetta and GTI applications, with related Audi, SEAT and Škoda platforms also appearing in catalogues. Confirm the exact vehicle by VIN.

Why must the cap and sensor connection be checked?

Pressure-cap design and coolant-level sensing are part of the reservoir assembly interface. A mismatch can prevent sealing, warning operation or correct hose routing.

What photographs help with fitment approval?

Send the moulded OE number, cap neck, connector, every hose port, mounting tabs and one overall image of the removed tank in its installed orientation.

Can AutoParts quote wholesale quantities?

Yes. Provide 1K0 121 407A, SKU VM01015-003, quantity, destination and packing requirements for a B2B quotation review.

Request a 1K0 121 407A Reservoir Quote

Send OE 1K0 121 407A, SKU VM01015-003, required quantity, destination and original-part evidence to AutoParts for application review and a wholesale proposal.

Fitment notice: OE and vehicle references support identification, but they do not replace VIN-, engine- or chassis-specific catalogue checks and direct comparison with the removed reservoir.

Inspection focus: Compare level-sensor connection, hose ports, cap seat and mounting tabs.

Supply note: Prepared for distributor samples, mixed cooling-system orders and export packing.