C-Tzu Thermostat Housing Assembly for BMW 1999–2006 (323/325/328/330/5/X/Z) Aluminum, 97°C Thermostat

C-Tzu's aluminium thermostat housing assembly is a direct-fit replacement for select BMW models (1999–2006), engineered to restore a sealed coolant path and reliable thermostat operation at 976C (206.66F).

This heavy-duty replacement housing is made from precision-cast aluminium and built to match OEM mounting points and fluid passages for an accurate, leak-free fit. It is compatible with a wide range of BMW engines and replaces multiple OEM part numbers (including 11537509227, 11531437040 and 11531436823), offering a practical service solution when the original plastic or corroded housing fails. The unit includes a thermostat opening temperature rating of 976C and is designed for straightforward installation with no special tools required.

Which BMW models and part numbers does this housing work with?

This C-Tzu assembly covers many BMW 3-, 5- and Z-/X-series vehicles produced between 1999 and 2006. It replaces a long list of OEM references so you can match it to your stamped part number or online parts listing.

• Compatible models: BMW 323, 325, 328, 330, 525, 528, 530, X3, X5, Z3, Z4 (1999–2006).
• Common replacement numbers: 11537509227, 11531437040, 11531436823 and related cross-references.
• Check your vehicle VIN or current housing part number to confirm fit before purchase.

How does installation work — do I need special tools or modifications?

The assembly is engineered as a direct OE-style swap, so no custom machining or adapter plates are required. Basic hand tools, coolant catch pan and fresh gasket or O-ring (if required) are all that’s needed for most installs.

• Remove the old housing, clean mounting surfaces, and replace the gasket or seal.
• Torque fasteners to manufacturer spec to avoid warping or leaks.
• Refill cooling system and bleed air according to BMW service procedures.

What are the material and performance details I should know?

Constructed from aluminium for improved heat tolerance and corrosion resistance compared with many OEM plastic housings, this unit is dimensionally accurate to maintain coolant routing and thermostat positioning. The thermostat opens at approximately 976C (206.66F) and the housing is designed to sustain a high-quality seal under normal operating conditions.

• Material: precision aluminium casting for strength and thermal stability.
• Thermostat activation: ~976C / 206.66F.
• High-tolerance fit to OEM mounting points and coolant passages.

Will this part prevent future coolant leaks and overheating?

Replacing a cracked or deteriorated housing with a robust aluminium assembly reduces the risk of leaks originating at the housing interface. While a new housing improves system integrity, follow-up checks on hoses, clamps, thermostat operation and coolant condition are recommended to ensure complete system health.

• Designed to restore a sealed connection between engine and coolant routing.
• Use fresh coolant and inspect hoses/clamps during installation.
• Perform a pressure test or road test to confirm leak-free operation.

Who is this for? If you own a compatible BMW from 1999–2006 and are replacing a cracked or leaking thermostat housing—or you prefer a more durable aluminium replacement over the original plastic part—this C-Tzu assembly is made for technicians, DIY enthusiasts and fleet managers seeking a precise, OEM-aligned repair. Always verify part numbers and vehicle compatibility before ordering and consult a qualified mechanic if you are unsure about installation or system flushing procedures.