Put new radiator in,and no heat comes out,Could my hearter core be froze up.

-Yes. If it's frozen. There is no water can run through the heater core. That's why no heat.
-How do you know it's frozen...? Did put just water into it. No antifreeze at all ? If so then it can crack the radiator or even the engine block as well.
Good luck

Mai

Bad head gasket.

I had a 91 GMC 4.3 do the same thing. Liked to froze to ***** one winter. Found I had a air bubble (air lock) in the engine block and heater. It was a bear to get out. Finally installed back flush kit in the heater hose between engine and heater. Took cap off flush kit, pour coolant in through outlet till coolant ran through back to radiator. Replaced cap and started engine. Repeated again. Heater works as good as new. It's using the same principle as priming a gas powered water pump.

How many miles are on the engine? It could be the radiator is clogged.

If a radiator leaks you buy a new one,common sense

The Stop Leak probably clogged your hearter core
Now you can remove that & try to clean it out or replace
it also

Subarus tend to block their radiators. Often there is only 10% or less flow. The radiator needs to be taken out and have a radiator shop strip and rod out the core tubes or fit a new or recored radiator.

IS COOLANT LEVEL LOW ? SEE IF BOTH HEATER HOSES ARE HOT
IF NOT TRY BACK FLUSHING HEATER CORE

a heater uses the temperature of the cars water, running threw a heat exchanger if the heater core has failed water will not circulate threw the engine properly this will and can cause over heating as well as nothing blowing from the heater. good luck.heater cores are generally inexpensive parts to replace.

last thing you can check if heater core is ok. is the thermostat.

Don't mess w/the drain plug, they are plastic and you will break it. Just pull the lower hose.

The heat will come from heated coolant running through you heater core. There are several reasons for no heat:
1) The heater core is blocked.
2) The coolant is not getting hot.
3) The coolant is low and not getting to the heater core.

Does the engine temperature gage show the engine temp is correct?
Is the coolant at the proper level?
Radiator cap could be bad - not holding pressure, but more likely would be low coolant or an open thermostat. An open thermostat will cause all of the coolant to circulate through the engine and therefore the engine temperature will be cooler than it should be.