Radiator over heating - overflow

1988 New Yorker 3L V6- I have replaced my thermostat, flushed the radiator but still it over heats. I noticed under the car quit a lot of fluid coming out and when I looked at the over flow container, it was coming out of an open stem. Is that normal? I loose fluid even driving around the block. Should there be aq cap over the stem?

A leakiy head gasket ot cracked head are most likely causes of such a problem.

Are you basing the overheating complaint simply on an overflowing radiator?
If so, maybe it’s not overheating at all and the radiator cap is weak.

If the car overheats, the dash should show a RED light as well to indicate a hot engine.