Welcome to 2CarPros.
If the engine isn't overheating and the coolant is coming out, we need top check for a bad head gasket. It sounds like compressed air from the combustion chamber is getting into the cooling system and causing this.
Take a look through this link and let me know the results.
https://www.2carpros.com/articles/head-gasket-blown-test
As far as the water pump working, if the engine doesn't overheat, it is working.
Let me know the results of the head gasket test.
Take care,
Joe
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Friday, April 26th, 2019 AT 8:28 PM