From some of the posts on here and resources left the native Oscar likes warm water but leathal temperatures are around 55 degrees Fahrenheit.
I also have a tank with local fish in it such as bull head cat, pumpkin seed sunfish a couple brookies and a few large shiners, and a few tropical, an Oscar be one of them. My tank reaches temps of almost 80 in the summer and not above 64 in the winter. Mostly because it’s kept in my garage