If I recall correctly, the 94-95 had the biggest issues with head gaskets. Ford claimed the problem was fixed for the 96-98 model year. This was achieved by using higher torque specs on the bolts. Your 96 should be good, obviously you are having and issue. The only thing that comes to mind would be to make sure they are torqued correctly. I see a lot of v6 mustangs with junkyard motor swaps. Is it the original motor in yours, or is it possible someone had previously swapped in a 94-95 3.8? Hell after my 94 had the head gasket go, it got a 98 3.8 swapped in to prevent further head gasket issues. It never had any problems engine wise. Everything else broke, but the motor was good.
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