How to Install a Coolant Expansion Tank on a 2000 BMW 323i

Removing the Existing Tank
1. Let the engine and radiator cool down completely. Open the hood and support it in a raised position.
2. Pull the electrical wiring harness from the back side of the air filter housing on top of the engine. Unsnap the two connectors on the intake hose on the back side of the air box. Remove the two retaining bolts on the driver’s side of the housing with a socket and ratchet. Lift the housing up and remove it from the engine bay.
3. Remove the retaining screws on the engine cover on the underside of the car with a Phillips screwdriver. Rotate the cover downwards so that you can access the underside of the radiator and expansion tank.
4. Remove the pressurized cap from the expansion tank slowly and place it aside. Place a clean drain pan under the driver’s side of the radiator. Remove the drain plug on the bottom of the radiator with a wrench. Replace and tighten the plug after all the coolant has drained from the radiator.
5. Unplug the wiring connector from the coolant sensor on the bottom of the expansion tank. Rotate the sensor counterclockwise and pull it straight out of the bottom of the tank. Place the sensor aside.
6. Pull straight out on the lever of the locking clip on the bottom of the tank until it stops. Pull straight up on the levers of the two locking clips on the coolant hoses on top of the expansion tank in the same manner. Pull the hoses toward the back of the car to detach them from the tank.
7. Pull the lever on the locking clip on the heater hose fitting -- located midway between the top and bottom of the tank -- toward the back of the car until it stops. Pull the heater hose straight off the tank.
8. Pull the tank straight upward until the tab clears the mounting plate on the bottom. Tilt the top of the tank toward the back of the car slightly, then pull it straight out of the engine bay.
Expansion Tank Installation
9. Insert the tab in the bottom of the expansion tank into the slot in the mounting plate near the bottom of the radiator. Tilt the top of the tank towards the radiator. Push the heater hose onto its fitting on the tank and push the locking clip inward.
10. Push in on the locking clip on the bottom of the tank. Insert the coolant temperature sensor into the hole in the bottom of the tank and twist it in a clockwise direction. Push the wiring connector into the terminal on the sensor.
11. Push the two coolant hoses onto the fittings on the top of the tank. Push the locking clips on the hoses downward.
12. Rotate the engine cover upwards and tighten the Phillips screws. Position the air filter housing back into the engine bay. Replace and tighten the two retaining screws. Push the intake hose onto the back of the housing and snap the two connectors together. Push the wiring connector on the plug on the back of the housing until it snaps into place.
13. Place a funnel into the opening of the coolant expansion tank. Loosen and remove the plastic bleed screw on the top of the expansion tank with a wrench. Place an additional drain pan under the expansion tank. Pour the coolant that was drained from the radiator into the funnel slowly until coolant with no air bubbles comes from the bleed screw opening. Tighten the bleed screw, remove the funnel and replace the pressurized cap on the tank.