SEAT Leon 1P 2005–2012
Thermostat Housing / Coolant Flange

Do not order this component from registration, model year or engine size alone.

This actual part is marked 03L 121 121 C / 038 121 121 D / 06A 121 121 C. These numbers, the physical shape, hose connections and your vehicle VIN should be checked before purchase.

Some SEAT Leon 1P 2.0 TDI applications use different coolant housings depending on engine code and engine-number production breakpoint. An alternative housing reference such as 03G121121D is found on other applications. If your removed component carries a different number or has different ports, do not assume this part will fit.

Unsure? Contact us through eBay messages with your full VIN, engine details and a clear photograph of your existing housing before ordering.

Actual Item Photographs

Reference Vehicle — SEAT Leon 1P 5-Door

These photographs are included only to help identify the Leon 1P five-door body shape. They are reference vehicles, not photographs of the donor vehicle.

Part Specification

Component	Thermostat housing / coolant flange / coolant pipe union
Main number	03L 121 121 C
Additional moulded numbers	038 121 121 D / 06A 121 121 C
Material marking	PA66-GF30 — glass-fibre reinforced polyamide 66
Condition	Used
Vehicle family	Selected Volkswagen Group applications — VIN verification required
Thermostat	Housing/flange only unless a thermostat is specifically shown as supplied
Seal / O-ring	Check photographs/listing contents; inspect sealing components before installation

SEAT Leon 1P Compatibility Guide

The table below identifies catalogue applications associated with this exact part-number family. It is deliberately more specific than a simple model-year search. Final fitment must still be confirmed from VIN, engine number and the removed part.

Other VAG Cross-Reference Families

The same reference-number family appears in selected applications across other Volkswagen Group platforms. These entries are provided as a cross-reference aid, not as automatic compatibility.

Platform	Fitment Status
Audi A3 8P / Sportback 8PA — selected 1.6 / 2.0 applications	VIN + old part number required
SEAT Altea / Altea XL 5P — selected 1.6 / 2.0 applications	VIN + old part number required
Skoda Octavia II 1Z — selected applications	VIN + old part number required
Volkswagen Golf / Golf Plus related platforms — selected applications	VIN + old part number required

Where Is This Part Fitted & What Does It Do?

This component forms part of the engine cooling circuit at the thermostat / coolant-outlet interface. It provides a sealed connection between the engine cooling passages and the connected coolant hosework.

The housing itself does not regulate temperature; the thermostat performs that function. The housing provides the mechanical connection and coolant seal. Exact mounting position and access route vary with engine code, which is why installation instructions and tightening data must be checked against the VIN.

Symptoms of a Damaged or Leaking Housing

• Visible coolant seepage or droplets around the flange/hose connection.
• Dried pink, white or coloured coolant residue around the joint.
• Repeated coolant-level loss or low-coolant warning.
• Coolant smell after driving.
• Leak appearing only when the cooling system is hot and pressurised.
• Air entering the system after coolant loss, potentially affecting heater performance.
• Temperature fluctuation or overheating if coolant loss becomes severe.

These symptoms can also be caused by other cooling-system faults. Correct diagnosis and a cooling-system pressure test are recommended before replacing components.

Why Choose a Factory-Produced Used Part?

A used factory-produced component retains the original moulding layout, hose geometry, fixing locations and material specification developed for its intended vehicle application. This can be particularly important on cooling-system fittings where port position, sealing surfaces and mounting geometry must match.

Lower-cost reproduction components can vary in material, mould quality and dimensional accuracy. Matching the original number and physical design gives you a far stronger basis for ordering correctly.

On some vehicle parts, buying used can save as much as 70% compared with the current price of an equivalent new component.

Actual saving varies by component, availability and current new-part pricing.

Typical Fitting Procedure

1. Allow the engine and cooling system to become completely cold.
2. Remove any engine covers or intake components required for safe access.
3. Drain or extract sufficient coolant so the level is below the housing.
4. Photograph and label connected hoses before removal.
5. Release hose clips/clamps carefully and disconnect the coolant hosework.
6. Remove the housing fasteners using the correct tool for your engine.
7. Remove the housing and old sealing element.
8. Clean the mating face without damaging the sealing surface.
9. Inspect the replacement housing, ports and mounting points against the old part.
10. Fit the correct sealing element and install the housing.
11. Tighten fasteners to the VIN/engine-specific manufacturer workshop specification. Do not guess a torque value.
12. Refill using the coolant specification approved for the exact VIN/engine. Do not select coolant purely by colour.
13. Bleed or vacuum-fill the cooling system as applicable.
14. Pressure-test, run to operating temperature and inspect carefully for leakage.
15. Allow the vehicle to cool and recheck the coolant level.

Typical Tools Required

• Socket set, ratchet and extensions.
• Torx / hex tools as required by the exact engine.
• Hose-clamp pliers.
• Small pick or hook tool for seals.
• Suitable coolant drain container.
• Torque wrench.
• Cooling-system filling funnel or vacuum-filling equipment.
• Cooling-system pressure tester.
• Protective gloves and eye protection.

Estimated Labour Time & Garage Cost Guide

A reasonable planning allowance for this type of housing replacement is approximately 0.5–1.5 labour hours, depending on engine configuration, access, corrosion, coolant filling procedure and whether additional components must be removed.

Because JavaScript/active calculators are not suitable for an eBay description, use the static labour-cost table below:

Labour figures are estimates only and exclude the part, coolant, diagnostics, ancillary components, disposal charges and additional repair work.

Professional Repair Support

Illustrative workshop stock photograph — not a photograph of ThePartPilot premises.

More Than 25,000 Parts On The Shelf

With more than 25,000 vehicle parts in stock at any one time, ThePartPilot focuses on supplying correctly identified used components and providing the information buyers need before fitting.

Illustrative warehouse stock photograph — not a photograph of ThePartPilot premises.

Collection Available 7 Days A Week

Collection is available 7 days a week until 8pm by prior appointment, including bank holidays where an appointment has been agreed in advance.

Please arrange collection through eBay messages before travelling. Seller business information and the appropriate collection details are available through eBay.

UK & International Delivery

International delivery is offered through the eBay Global Shipping Programme / eBay International Shipping where available for this listing and destination. The shipping services, destination eligibility, import charges and delivery options shown by eBay at checkout are definitive.

Current GSP destination guide

EU: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Poland, Portugal, Romania, Slovakia, Slovenia, Spain and Sweden.

Other listed destinations: Antigua and Barbuda, Aruba, Australia, Bahamas, Bahrain, Bangladesh, Barbados, Belize, Bermuda, Bolivia, Brazil, Brunei Darussalam, Cambodia, Canada, Cayman Islands, Chile, China, Colombia, Costa Rica, Dominica, Dominican Republic, Ecuador, Egypt, El Salvador, French Guiana, Grenada, Guadeloupe, Guatemala, Guernsey, Honduras, Hong Kong, Iceland, Indonesia, Israel, Jamaica, Japan, Jersey, Jordan, Kuwait, Liechtenstein, Macau, Malaysia, Maldives, Martinique, Mexico, Monaco, Montserrat, New Zealand, Nicaragua, Norway, Oman, Pakistan, Panama, Paraguay, Peru, Philippines, Qatar, Reunion, Saint Kitts and Nevis, Saint Lucia, Saudi Arabia, Singapore, South Africa, South Korea, Sri Lanka, Switzerland, Taiwan, Thailand, Trinidad and Tobago, Turks & Caicos Island, United Arab Emirates, Ukraine, Uruguay, United States and Vietnam.

eBay programme coverage changes over time. Always rely on the destination and service presented at checkout.

How to find us / WhatsApp

Scan the QR code to open a WhatsApp chat for collections and enquiries.

If the QR image needs refreshing, generate it again from the same WhatsApp link.

Returns & Fitment Responsibility

We provide part numbers, photographs and compatibility guidance to help customers order the correct component first time. If you are uncertain, please ask us to check your VIN and existing component before installation.

Parts & Accessories should be returned in the same condition in which they were supplied. Installation, alteration, damage, missing components or use can reduce the value of a returned item.

Where eBay policy permits a seller deduction for an item returned in a different condition, any deduction will reflect the actual loss in value and be handled in accordance with eBay's applicable return rules. There is no automatic fixed 50% fee based solely on the selected return reason.

VAT / Global Accounting

Where this used item is sold under our applicable HMRC Global Accounting / second-hand margin arrangements, VAT is accounted for under the relevant scheme and is not separately itemised.

♻ Support Small Business • Reuse More • Waste Less

Choosing a serviceable used vehicle part can keep an existing component in productive use rather than unnecessarily consuming another newly manufactured replacement. Reuse can reduce demand for raw materials, manufacturing, packaging and disposal while helping keep vehicles economically repairable.

🔧 Correct part identification  •  ♻ Reuse  •  📦 Careful dispatch  •  ✅ Small-business service

Thank you for supporting ThePartPilot and the circular use of quality vehicle components.

Carefully Prepared For Dispatch

Parts are prepared for transport with the aim of protecting mounting points, electrical connections and vulnerable surfaces during delivery.

Illustrative dispatch image — not a photograph of the actual parcel or ThePartPilot premises.

Compare 03L121121C / 038121121D / 06A121121C, the housing shape and hose connections with your original component.

For definitive confirmation, contact us through eBay messages with your 17-character VIN + existing part number + clear photograph.

Reference SEAT Leon photographs: Thomas doerfer, Wikimedia Commons, CC BY-SA 3.0.
Workshop / warehouse illustrative photographs: Nenad Stojković / Shixart1985, Wikimedia Commons, CC BY 2.0.
Dispatch illustration: VCCmatt, Wikimedia Commons, CC BY-SA 4.0.
Actual product photographs: this ThePartPilot eBay listing.