C-Tzu Aluminium Thermostat Housing Assembly for BMW 1999–2006 – Direct-Fit, 97°C Thermostat

C-Tzu’s aluminum thermostat housing assembly is a direct-fit replacement built to restore proper coolant control on select BMW 323, 325, 328, 330, 525, 528, 530, X3, X5, Z3 and Z4 models from 1999–2006.

This heavy-duty assembly replaces multiple OEM part numbers and is engineered to match original mounting points and coolant passages so you can quickly replace a leaking or failed thermostat housing. Machined from aluminum with a precision thermostat calibrated to open at approximately 97 °C (206.6 °F), the unit is intended to provide a reliable seal and long service life under normal operating conditions.

How will this assembly fit my BMW and which part numbers does it replace?

The C-Tzu housing is manufactured to meet the dimensional and mounting specifications of the original equipment for the listed BMW models. It is designed as a bolt-on replacement so you won’t need modifications to your vehicle’s coolant system.

• Replacement for OEM numbers: 11537509227, 11531437040, 11531436823 and related variants.
• Engineered to match original bolt pattern and hose connections for direct installation.
• Compatible with 1999–2006 BMW models including 3-series, 5-series, X3, X5, Z3 and Z4.

What materials and thermostat specifications are used in this unit?

The housing is constructed from aluminum for improved thermal conductivity and resistance to corrosion compared with lower-grade materials. The thermostat element is set to open at roughly 97 °C to regulate coolant flow at standard operating temperatures.

• Aluminum construction for durability and consistent heat transfer.
• Thermostat opening temperature: approximately 97 °C / 206.6 °F.
• High-tolerance machining for accurate sealing surfaces and fitment.

How straightforward is the installation and what tools will I need?

This part is designed as a direct OEM-style replacement, so installation is typically straightforward for anyone with basic automotive tools and mechanical experience. You’ll remove the old housing, swap in the new unit, and torque fasteners to factory specifications.

• No special tools or custom modifications required for most installs.
• Basic tools: metric socket set, torque wrench, coolant drain pan and new gasket or sealant as recommended.
• Follow vehicle service manual torque specs and bleeding procedure for the coolant system.

What performance and reliability can I expect from this C-Tzu housing?

The assembly is designed to reduce the chance of coolant leaks and provide stable thermostat operation when installed correctly. Proper sealing surfaces and corrosion-resistant aluminum construction contribute to longer service intervals under normal conditions.

• High sealing capability to help prevent leaks at the housing flange and hose connections.
• Durable design intended for long-term service when used with correct installation practices.
• Backed by a 30-day satisfaction guarantee for peace of mind after purchase.

Who is this for: The C-Tzu aluminum thermostat housing assembly is aimed at DIY mechanics and professional technicians working on BMW E46, E39, E53, E83, and related platforms from 1999–2006 who need a reliable, OEM-compatible replacement. It’s suitable for owners addressing leaks, overheating caused by failed housings, or anyone restoring coolant-system integrity with a direct-fit aftermarket option.