Expansion tank leak

[Joblack]

I took the Z for it’s weekly drive today and had a major coolant leak. I noticed a very small amount of steam rise from the front of the car when I stopped at an intersection. The temperature showed normal in the middle of its range. I pulled over when safe to do so and opened the hood to see a wet mess of coolant around the front of the engine. When I added water to the expansion tank I saw that most of what I added was leaking out from the lower area of the expansion tank. I drove the car home as this was not far from my house by driving for about 2 minutes and pulling over to fill the tank a few times. The temperature gauge never showed the car getting hot. Once home I removed the expansion tank and noticed a large crack down the side of it as well as an internal crack above where the transmission cooler piece fits. Mine lifted off easier than I expected after watching YouTube videos indicating that they usually are very stubborn to remove.
I will order an aftermarket replacement tank - are there any brands that are recommended?
Do the tanks include O- rings for the coolant hoses or do you get them separately?
I was very concerned how little coolant came out when I drained the tank… is there another drain for the cooling system? The car ran fine getting home but I worry about how little coolant came out when I drained it.
I have been servicing cars for years but am new to BMW’s, any tips are appreciated

 

[smorris_12]

To properly empty a car of coolant there's a drain screws in the bottom of the engine block and the lower radiator hose.

 

[enuff_zed]

If you are sure the coolant isn't that old then I would simply replace what you lose when the tank comes off. Last one I did took 2 litres of coolant to replace what I lost.
Put the front end of the car up high on jacks or ramps and it'll minimise your loses, plus you'll be able to get underneath if needed to push it off.

The tank should have it's own o-rings fitted where it push-fits onto the base plate.
The hoses come complete with o-rings in them. Not sure you can get them separately?

 

[enuff_zed]

Oh, one other thing? Auto or manual?
If it's an auto you'll need to get a new oil cooler thermostat that sits inside the bottom of the tank as the old one is very likely to fall apart.

 

[Joblack]

Thank you for the replies. I will change out all of the coolant while working on the car. I am concerned about the amount of antifreeze left in the coolant after adding so much water nursing the car home as we have some freezing temperatures in the weather forecast. I drained the radiator after work today and saw some antifreeze :?
The past expansion tank was a Cool Xpert with a build date of 08/2014.
The car is an automatic so I will take the advice of replacing the thermostat. Thanks again

 

[enuff_zed]

The car is an automatic so I will take the advice of replacing the thermostat. Thanks again

It's a cylindrical black thing about an inch in diameter and 3 inches long. It has a big spring inside and over time the plastic weakens. When you remove the tank the spring bursts the plastic apart. Mine nearly took my eye out!!
Part number is 17111437362

 

[Joblack]

I have a feeling mine wants to have a go at my eye as well…
It appears crooked and can be pushed flat. The plastic area of the expansion tank that houses it is cracked as well.
Thanks again for sharing your knowledge