Mustang blows coolant/water out of radiator cap

1995 Ford Mustang 3.8 - 126,000 miles
It runs fine at times and then at other times it blows coolant or water from the radiator cap. You can see where it shoots out. The car then starts to run hot. Recently put a new thermostat and new head gasket on car. No water is leaking from the exhaust like it was when I had a blown head gasket. What could be causing this?