Water goes into the engine mixes with oil

It will overheat eventually, It sounds like you have a blown head gasket.

Here are a couple of guides to get us started:

https://www.2carpros.com/articles/head-gasket-blown-test

and

https://www.2carpros.com/articles/coolantantifreeze-in-the-engine-oil

Please let us know what you find.

Cheers, Ken