1995 Geo Tracker change the theromstat and heater core no heat in the car when running water ain't flowing though the raditior with thermostat in it. but take it out the water flows so What is wrong?

sounds like you installed new thermostat upside down

if that's not the problem, you have wrong or faulty new thermostat

to test thermostat out of vehicle, place in pot of boiling water and watch to see if thermostat opens