Rear engine coolant leak

I have a 4.6 v8 2002 explorer xlt that's
been getting hot while driving. Thermostat
reads in the middle but decided to change
it anyway. When I finished loosening the
thermostat housing I had a pin hole
coolant leak out the rear passenger side of
the engine ! Now with the side steps and
having no jack or stands I couldn't really
get under for a look.
It only leaks when I release pressure from
the thermostat housing. How can I tell if it's
a hose or gasket I can't see, or if I
overheated and warped my head ??