BMW E46 3 Series, E53 X5 & E83 X3 LCI Aluminum Coolant Expansion Tank Reservoir Kit – Metal Radiator Overflow Header Tank, Cooling System Replacement | Replaces Part No. 17117573781

Upgrade your BMW's cooling system with this aluminum coolant expansion tank reservoir, designed as an aftermarket replacement for select BMW E46 3 Series, E53 X5, and E83 X3 vehicles using the coolant reservoir identified by BMW part number 17117573781. The expansion tank is an essential component of the pressurized engine cooling system, accommodating coolant expansion as engine temperature rises while providing a designated location for coolant level monitoring and system filling. This aluminum replacement offers a metal alternative to the original plastic reservoir design, making it an appealing option for BMW owners replacing an aging, cracked, or leaking factory coolant tank.

BMW cooling systems operate under controlled pressure and experience repeated heating and cooling cycles during normal driving. Over time, the original plastic expansion tank can become brittle due to engine compartment temperatures, pressure fluctuations, and material aging. Cracks may develop around molded seams, hose connections, mounting areas, or other stressed sections of the reservoir. These failures can result in coolant leakage, declining coolant levels, and an increased risk of engine overheating.

This replacement coolant expansion tank is designed around the original reservoir application associated with BMW part number 17117573781. Its aluminum construction provides a metal alternative to the original plastic tank body while retaining the intended function of accommodating coolant expansion and supporting the vehicle's cooling system. Proper connection geometry, sealing surfaces, cap compatibility, and coolant level sensor provisions are essential for successful installation.

The expansion tank works with the radiator, thermostat, water pump, coolant hoses, and pressure cap to maintain proper cooling system operation. As coolant heats up and expands, the reservoir accommodates the resulting volume changes. When the engine cools, coolant volume decreases. The expansion tank and pressure cap are part of the system that manages these temperature-related changes.

For BMW owners maintaining an older E46, X3, or X5, replacing a deteriorated coolant expansion tank can help address a common source of coolant loss. An aluminum replacement may offer different durability characteristics from the factory plastic design, although overall reliability still depends on the quality of the tank's fabrication, welds, connections, seals, and installation.

Whether restoring an aging cooling system, replacing a leaking reservoir, or selecting a metal expansion tank for a street-driven or performance-oriented BMW, this replacement provides an alternative to the original plastic component while preserving the intended coolant reservoir function on correctly matched vehicles.

Key Features

• Aluminum Tank Construction: Features an aluminum reservoir body as an alternative to the original plastic coolant expansion tank design.

• BMW E46, E53 & E83 Applications: Intended for select BMW 3 Series, X5, and X3 vehicles using the corresponding factory expansion tank configuration.

• OEM Reference 17117573781: Designed as an aftermarket replacement for the BMW coolant expansion tank identified by part number 17117573781.

• Supports Coolant Expansion Management: Accommodates coolant volume changes that occur as the engine heats up and cools down.

• Helps Restore Cooling System Integrity: Replacing a cracked or leaking reservoir can eliminate coolant loss originating from the original tank.

• Metal Alternative to Aging Plastic: Offers an aluminum tank body for owners seeking a different construction material from the original molded plastic reservoir.

• Designed for Pressurized Cooling Systems: Intended to function within the corresponding BMW cooling system when equipped with the correct pressure cap, connections, and seals.

• Factory-Style Installation Location: Designed to replace the original coolant expansion reservoir in its designated engine compartment position on compatible vehicles.

• Supports Coolant Level Monitoring: The correct replacement configuration must accommodate the vehicle's applicable coolant level sensor and mounting arrangement.

• Suitable for Cooling System Maintenance: Can be installed during cooling system refurbishment involving hoses, radiator components, thermostat replacement, or water pump service.

Replacing a deteriorated coolant expansion tank is an important part of maintaining a reliable BMW cooling system. This aluminum reservoir provides an aftermarket alternative to the original plastic tank and is intended to help restore proper coolant containment and expansion capacity when installed on a compatible vehicle.

FITMENT: BMW E46 3 Series, E53 X5 & E83 X3

BMW E46 3 Series Sedan

• BMW E46 320i – Select 2001–2005 applications

• BMW E46 323i – 1999–2000

• BMW E46 325i – 2001–2005

• BMW E46 325xi – 2001–2005

• BMW E46 328i – 1999–2000

• BMW E46 330i – 2001–2005

• BMW E46 330xi – 2001–2005

BMW E46 3 Series Coupe

• BMW E46 323Ci – 2000

• BMW E46 325Ci – 2001–2006

• BMW E46 328Ci – 2000

• BMW E46 330Ci – 2001–2006

BMW E46 3 Series Convertible

• BMW E46 323Ci Convertible – Select early applications

• BMW E46 325Ci Convertible – 2001–2006

• BMW E46 330Ci Convertible – 2001–2006

BMW E46 3 Series Touring/Wagon

• BMW E46 323i Touring – Select markets

• BMW E46 325i Touring – 2001–2005

• BMW E46 325xi Touring – 2001–2005

BMW E53 X5

• BMW E53 X5 3.0i – M54B30 3.0L, approximately 2001–2006

BMW E83 X3 – Pre-Facelift

• BMW E83 X3 2.0i – N46 2.0L, select markets

• BMW E83 X3 2.5i – M54B25 2.5L

• BMW E83 X3 3.0i – M54B30 3.0L

BMW E83 X3 LCI – Facelift

• BMW E83 X3 2.0i – N46 2.0L, select markets

• BMW E83 X3 2.5si – N52-family 2.5L, select markets

• BMW E83 X3 3.0si – N52-family 3.0L

Important Fitment Information

BMW's original expansion tank part number 17117573781 is documented across E46, E53, and E83 applications. However, the fitment of the original BMW plastic tank does not independently guarantee that every aftermarket aluminum version will clear surrounding components or accept all original connections.

For the aluminum replacement, customers must confirm:

• Original BMW reservoir part number

• Vehicle VIN and production date

• Engine configuration

• Transmission-related cooling system configuration

• Reservoir mounting arrangement

• Hose connection positions

• Coolant level sensor compatibility

• Pressure cap compatibility

BMW E46 M3 models are not included in this listing. The E46 M3 uses a different cooling system arrangement and should not be assumed compatible.

BMW E53 X5 V8 and diesel models are also not included in the confirmed scope of this listing.

Engine Compatibility

BMW M52TU Inline-Six Engines

• M52TUB25 – 2.5L gasoline

• M52TUB28 – 2.8L gasoline

BMW M54 Inline-Six Engines

• M54B22 – 2.2L gasoline

• M54B25 – 2.5L gasoline

• M54B30 – 3.0L gasoline

BMW N46 Four-Cylinder Engines

• N46-family 2.0L gasoline engines in select E83 X3 applications

BMW N52 Inline-Six Engines

• N52-family 2.5L gasoline engines in select E83 X3 LCI applications

• N52-family 3.0L gasoline engines in select E83 X3 LCI applications

Additional E46 Engine Variants

Certain four-cylinder E46 vehicles may also use the original BMW expansion tank reference, but exact aftermarket aluminum tank compatibility must be verified individually.

OEM Replacement Part Numbers

Primary BMW Reference

• 17117573781

• 17 11 7 573 781

Documented Earlier BMW References

• 17137787039

• 17111436413

The primary BMW part number 17117573781 supersedes earlier expansion tank references in the original BMW parts catalog.

These references identify the factory coolant expansion tank application. They do not establish that the aluminum replacement is manufactured by BMW or that it has identical material construction.

Installation

1. Park the vehicle securely on a level surface.

2. Switch off the engine and allow the cooling system to cool completely.

3. Never remove the coolant expansion tank cap while the engine is hot or the system is pressurized.

4. Confirm the replacement aluminum tank matches the original reservoir configuration.

5. Inspect the new tank for visible damage, incomplete welds, damaged fittings, or irregular sealing surfaces.

6. Remove any engine covers, intake components, or surrounding trim required for access.

7. Locate the original coolant expansion tank.

8. Inspect the original reservoir for cracks, leaks, coolant residue, or damaged connections.

9. Position a suitable drain container beneath the cooling system.

10. Drain the required amount of coolant according to the applicable BMW service procedure.

11. Disconnect the coolant level sensor electrical connector, where fitted.

12. Remove the coolant level sensor if it must be transferred to the replacement tank.

13. Carefully disconnect the coolant hoses and retaining clips from the original reservoir.

14. Avoid damaging brittle plastic hose fittings during removal.

15. Release the reservoir from its mounting bracket or retaining mechanism.

16. Remove the original expansion tank from the vehicle.

17. Compare the original and replacement tanks for height, width, connection positions, mounting points, and clearance.

18. Verify that the replacement tank accepts the correct pressure cap.

19. Confirm compatibility with the original coolant level sensor or the sensor supplied with the replacement, if applicable.

20. Inspect all required O-rings, sealing rings, hose fittings, and retaining clips.

21. Replace damaged seals and connectors before installation.

22. Install the replacement aluminum tank in the designated mounting location.

23. Secure the tank using the appropriate mounting arrangement.

24. Reconnect all coolant hoses to their corresponding fittings.

25. Ensure that each hose is properly seated and securely retained.

26. Reinstall or connect the coolant level sensor where applicable.

27. Verify that the tank and hoses do not contact moving components or interfere with surrounding engine parts.

28. Reinstall any removed engine covers or intake components.

29. Refill the cooling system using coolant that meets the vehicle's applicable BMW specification.

30. Bleed the cooling system according to the correct vehicle-specific procedure.

31. Inspect the reservoir, welds, fittings, and hose connections for coolant leakage.

32. Monitor engine temperature while confirming normal cooling system operation.

33. Allow the engine to cool and recheck the coolant level.

34. Perform a cooling system pressure test when appropriate.

35. Reinspect the reservoir and surrounding connections after initial operation.

Important Cooling System Safety Information

The BMW cooling system operates under pressure and can cause serious burns if opened while hot.

A leaking expansion tank can result in rapid coolant loss and engine overheating.

Do not continue driving if the vehicle overheats, coolant loss is substantial, or the replacement tank cannot maintain a secure seal.

Aluminum construction does not eliminate the need to inspect hose fittings, seals, radiator components, and the pressure cap.

Compatibility Notes

• BMW Part Number 17117573781: The primary OE reference identifies a coolant expansion tank used in select E46, E53, and E83 cooling systems.

• Aluminum Aftermarket Construction: This product is described as an aluminum replacement. The original BMW expansion tank is plastic. Do not describe the aluminum version as a factory BMW aluminum tank.

• BMW E46 Non-M Applications: The OE reference covers multiple non-M E46 3 Series configurations. Exact aluminum replacement fitment must be verified.

• BMW E46 M3 Exclusion: Do not advertise E46 M3 compatibility without a separate verified application.

• BMW E53 X5 Compatibility: The documented X5 application is the E53 X5 3.0i with the M54 inline-six engine.

• BMW E53 V8 Exclusion: Do not assume compatibility with the X5 4.4i, 4.6is, or 4.8is.

• BMW E83 X3 Compatibility: The OE reference is associated with select first-generation X3 vehicles.

• BMW E83 LCI Compatibility: BMW catalogs include facelift E83 X3 applications, including select N52-powered models.

• Not All X3 Engines Are Included: Diesel and other engine variants require individual part-number confirmation.

• Transmission Configuration Matters: BMW cooling system layouts can vary with manual and automatic transmission equipment. Verify the original reservoir and associated mounting arrangement.

• Check the Reservoir Mounting Bracket: The aluminum tank must fit the original mounting location without interference or unsupported modification.

• Verify Hose Connection Geometry: The replacement tank must match the original coolant hose positions, connector diameters, and sealing arrangements.

• Check Pressure Cap Compatibility: The reservoir must accept a pressure cap with the correct specifications for the vehicle.

• Pressure Cap May Be Sold Separately: Do not assume that a radiator or expansion tank pressure cap is included.

• Coolant Level Sensor Compatibility: Verify that the aluminum tank supports the required sensor configuration and that the sensor operates correctly after installation.

• Coolant Level Sensor May Be Sold Separately: The original BMW tank is commonly supplied without the sensor. Confirm the actual aluminum product's package contents.

• Sealing Rings and O-Rings: Confirm that all required seals are included or available separately. The OE tank reference does not guarantee that every seal is supplied.

• Tank Material Does Not Guarantee Better Cooling: An aluminum expansion tank does not automatically reduce engine operating temperature or increase radiator cooling capacity.

• No Guaranteed Elimination of Cooling Problems: Replacing the reservoir will not correct a defective thermostat, water pump, radiator, cooling fan, or unrelated coolant leak.

• Inspect Existing Coolant Hoses: Aging hoses may crack or leak when disturbed during reservoir replacement.

• Inspect the Thermostat: A malfunctioning thermostat can cause overheating independently of the expansion tank.

• Inspect the Water Pump: Water pump failure or leakage can cause coolant circulation problems and overheating.

• Check the Radiator: A leaking or restricted radiator requires separate diagnosis and repair.

• Correct Coolant Required: Use coolant meeting the applicable BMW specification and follow the vehicle's specified mixture requirements.

• Proper Bleeding Is Essential: Air trapped in the cooling system can cause overheating, inconsistent heater performance, or abnormal coolant level behavior.

• Corrosion Compatibility: The replacement tank's aluminum construction must be suitable for the vehicle's coolant chemistry. Use the correct coolant and avoid incompatible additives.

• Weld Quality Matters: Aluminum tank reliability depends partly on weld integrity, manufacturing quality, and sealing surfaces. Inspect the actual product before installation.

• No Verified Tank Capacity: Do not advertise a specific reservoir volume without confirmed product specifications.

• No Verified Aluminum Grade: Do not claim a particular aluminum alloy, wall thickness, or fabrication process unless documented by the supplier.

• No Verified Pressure Rating: Do not advertise a maximum operating pressure without manufacturer documentation.

• Not a Complete Cooling System Kit: This listing covers the coolant expansion reservoir, not the radiator, thermostat, water pump, or complete hose system.

• Confirm Included Components: The cap, coolant level sensor, mounting hardware, seals, and hoses must be listed separately unless confirmed as included.

• Original BMW Supersessions: Earlier OE references include 17137787039 and 17111436413. These apply to the original BMW parts catalog and do not independently verify the physical fit of every aftermarket aluminum version.

• OEM Reference vs. Genuine BMW: This is an aftermarket aluminum replacement and should not be described as Genuine BMW.

• VIN Verification Recommended: Confirm the vehicle's original reservoir part number, production date, transmission configuration, and cooling system layout before purchasing.

Long-Term Cooling System Reliability

Maintaining a properly sealed coolant expansion tank is essential for the reliability of BMW E46, E53 X5, and E83 X3 cooling systems. As original plastic reservoirs age, repeated pressure and temperature cycles can contribute to cracking, coolant seepage, and unexpected fluid loss.

This aluminum coolant expansion tank provides a metal replacement option for compatible vehicles using BMW part number 17117573781. When manufactured to the correct specifications and properly installed, it can help restore coolant containment and maintain the intended expansion reservoir function.

For BMW owners replacing aging cooling system components or undertaking a comprehensive cooling system refurbishment, selecting the correct reservoir, inspecting related hoses and seals, using the proper coolant, and thoroughly bleeding the system are essential steps toward dependable engine cooling performance.

Please refer to the “Fitment” section in the product description for compatibility details.