this may sound crazy but crack about 2 or 3 eggs in it ,it worked in my 90 model escort.
vacuum leak
radiator leak. try adding " leak stop"
water leak or bad thermostat
Remove the radiator and take it to a radiator shop.
Cooling lines from transmission to radiator?
look for antifreeze coming out of the radiator as the engine warms up after a cold start.
Coolant leak? Check your heater core.
you may have a loose seal or a pinhole leak i would get it checked out asap
If the radiator was not fitted in properly or the pipes were not attached correctly, the radiator would leak.
The simple and really only answer I can give you is to find the leak and repair it.
Leaking radiator radiator hose head gasket water pump Heater core thermostat housing
Mostly untight hose clamps or a hairline crack on the radiator drives side. Coolant will also leak from a faulty water pump