I have water pouring out under my 1995 Mustang 3,8 on the passenger side as fast as I can put it in
Check the heater hoses,if it is coming from intake or block you may have bad gaskets.
Sounds like a heater core to me. Anti-freeze used in cars becomes highly corrosive in cars that set and are not started for extended periods of time. This can ruin the heater core and the radiator.
Also, check your core plugs in the block. They deteriorate and rust through causing a leak like you describe.
Looking for a Used Mustang in your area?
CarGurus has 35,434 nationwide Mustang listings starting at $1,200.
Search Ford Mustang Questions
Ford Mustang Experts