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Expansion Tank Replacement
BMW 540i (E39)
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The expansion tank is just right behind the radiator tank.

Start by pulling out all plastic rivets. Use a flathead screwdriver to pop them out.

There is another on the passenger side as shown here

Unscrew the Expansion Tank Cap.

WARNING: Do not attempt this when the engine is still hot!

Unscrew this plastic screw

Take out the plastic tab strip that holds that expansion tank to the fan shroud by pinching both locking tabs inwards at the same time and then pulling it out.

Using a flat head screwdriver, proceed to take out the plastic screw

To make room in taking out the Expansion Tank, remove the Air Filter box cover by unsnapping all locking tabs as shown, and also pulling out the Sensor.

You also need to unlock this tabs to finally take out the Air Filter box

Pull out the Sensor by squeezing the retaining tabs as shown

When all locking tabs are unsnapped and the Sensor is taken out from the Filter Box cover, gently pull the cover as shown while twisting it back and forth

With the Filter Cover box off, you will now have more room to work on in between.

Proceed to loosen the clamp and pull the Expansion Tank off from the lower tube.

Slide the Expansion Tank away from the Fan Shroud to expose another tubing. Loosen the clamp and pull this tubing off the Expansion Tank.

The Expansion Tank sits on a ledge at the bottom of the Fan shroud.

Slide the tank away from the fan shroud while lifting the tank up. Take notice of the protruding notches of the tank and holes of the ledge where both mates.

With the Expansion Tank completely off, lift up and pull out the Fan shroud.

Pull out and lift the Expansion Tank to expose the Sensor and wiring at the bottom. Pull out the Sensor wiring harness while squeezing on the retaining tabs.

With the Expansion Tank upside down, firmly hold the body of the Sensor assembly and turn counter-clockwise to loosen it.

WARNING: The Sensor might break if not properly supported.

This is the unlocked position. Carefully slide out the Sensor Assembly out of the tank.

Set aside the Sensor assembly for later re-assembly on the new tank.

Install the Sensor to the new tank and proceed to reinstall everything back

When the new Expansion Tank is in place, fill it up with coolant. Refer to your manuals on how to top this up. You will need to run the engine in between refills just enough to cycle the coolant through.

Depending on how much coolant was initially lost, you might want to prepare about 2 gallons of coolant. That is how much I spent on coolant anyways!

And... you're done!

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