Help. Coolant problem

[Bmw321]

What is happening here?

https://www.youtube.com/shorts/GwVEXs81gHs
https://www.youtube.com/shorts/7srGHaLRGgs

I had an coolant leak probably from the temperature sensor. (13621433077).
I changed the sensor and the hose (17127509963).

Now this happens. It seems like pressure and air build up. First time I tigthen the expansion tank cap. Then the expansion tank broke.
It starts to happen when the engine gets hot

[X5only]

The basics:
1) Did you bleed the system?
2) Is the water pump working?

[Bmw321]

1) I opened the bleeder screw at the coolant expansion when I was filling the system and a couple of times just after the filling when the engine have been running some time.
2) I suppose. Constant and normal collant temperature when the engine is warm

[andrewwynn]

Test for exhaust gases


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[X5only]

Originally Posted by Bmw321

1) I opened the bleeder screw at the coolant expansion when I was filling the system and a couple of times just after the filling when the engine have been running some time.
2) I suppose. Constant and normal collant temperature when the engine is warm

Sorry, meant the auxiliary water pump.

[Fifty150hs]

Originally Posted by andrewwynn

Test for exhaust gases


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+1 Looks like a blown head gasket.

[andrewwynn]

Did you have the coolant dump while running when the leak happened? It doesn't take long for catastrophic overheat