The radiator does have a drain plug as I recall.

It is straight up from the bottom on the drivers side to the best of my memory.

You may need to remove the lower engine cover to gain access.

I would probably remove the lower engine cover anyway because you will lose coolant when you pull the lower hose and water pump. It will also keep you sane when you drop bolts, nuts and tools in the BMW Black Hole!

I did not pull the fan or the upper cross bar, but might recommend doing this.

I am in the process of replacing my Voltage regulator and had to pull the fan and upper cross bar, not too hard, you just need to figure out how to release the fan shroud and then fold the small arm on the drivers side in to make the fan easier to remove. You should also pull the 4 screws that hold the top radiator cover so you can easily remove the fan shroud ears.

I would also recommend replacing the O-ring on the fan sensor that is located near the lower radiator hose. BMW part #13621743299.

If you decide to replace the serpentine belts, this can be a PITA due to the cage over the power steering/active suspension pump. Not sure if this is the same on models without the active suspension.

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2008 4.8i Black with Tabacco. Black Y-spoke wheels and shadowline trim.