water mixing with oil engine

Sounds like a compromised head gasket.

A cooling system pressure test will probably confirm it.

Some parts store will "rent" you the tool to do it, "rent" really meaning "Deposit", in which you get all of your money back when you return the tool. So really, you use it for free.

The Medic

Here are a couple of guide that will help you get the job done.

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

and

https://www.2carpros.com/articles/radiator-pressure-test

Please let us know what happens.

Best, Ken