91 grand prix need help

I have a leak.But the leak problem is on the metal not a hose or something simple:disappoin .Now my question is there any kind of "patches" or anything to put on metal leaking problems??Its a 3.1.The water leak is under the thermostat and the hole is about 5mm long on metal.

This is very easy. There is many different products that will seal this well. There is a putty made for exaust manifolds that will tolerate temps to over 2000 degrees. There is J.B. Weld. There are many more that would take hours to list. Just go to a place like Parts America, or AutoZone, or something of that nature and they can give you the best product of your area of repair.

If the leak is on the "quick connect" heater hose fitting that goes in to the intake just below the t-stat housing, metal mend epoxy will not fix the problem. Those fittings are known to rot from the inside, turn mushy, and fail. It will only get worse, and epoxy will only make replacing it harder.