How to Replace Oil Cooler Thermostat 01-05 BMW 325Xi

Difficulty: Advanced · About 130 min · Bmw 325xi

Replace the oil cooler thermostat on a 2001–2005 BMW 325Xi by draining coolant and removing the fan, air box, and expansion tank for access, then bleeding the system after reassembly.

Steps

1. Disconnect the battery and remove the fan

   Disconnect the negative battery cable. Remove the air collector and fan shroud retainers, unplug the fan connectors, then loosen the reverse-threaded fan clutch with the correct wrench and lift the fan and shroud out together.

2. Remove the air box

   Unplug the mass airflow sensor, loosen the intake clamp, and separate the air tube. Release the air box clips, remove its lid and filter, undo its mounting bolts, and lift the box clear.

3. Drain coolant and remove the reservoir

   With the engine cold, remove the reservoir cap and drain coolant into a pan. Release the radiator and reservoir hose retainers, remove the reservoir fasteners, unplug its level sensor, and lift the reservoir out.

4. Replace the oil cooler thermostat

   Remove the old thermostat and install the replacement using its keyway for alignment. Reconnect the level sensor and reservoir, secure the hoses and retainers, and reinstall the reservoir fasteners.

5. Reinstall the fan and air box

   Lower the fan and shroud into position and secure the clutch to the vehicle's specification. Reinstall its retainers and connectors, fit the air box and filter, reconnect the intake and sensor, then reconnect the battery.

6. Refill and bleed the cooling system

   Use the specified coolant and follow the vehicle's bleeding procedure at the reservoir bleed screw. Run the engine with the heater on while monitoring temperature and level, then let it cool fully and recheck for leaks and correct coolant level.

Check your vehicle’s repair manual for exact specifications and fit.