Losing coolant in a vehicle is not a good thing. It is best to check all seals and all bends in tubing.
if it is coolant and not condensation. I would say you have a blown head gasket. the coolant will smell sweet. but if it is a bad head gasket it will run hot also.
I think you would know if you needed a freeze out plug for you would be losing coolant & losing coolant would make your ride run hot.
Because the coolant is low.
Obviously, you are losing coolant from some part of the system. Did you do a pressure check or did you simply do a visual inspection? Coolant may be lost by evaporation or you may have a gasket leak which would allow coolant to transfer to the engine oil. Check the oil dipstick after the car has run long enough to get it to an operating temperature where the thermostat has opened up. If the oil looks foamy, I would do a cylinder pressure check. If the values you get are more than 10 pounds different, I would suspect you have a blown head gasket.
Leak in heater core
Not sure but, if it does have a bleeder it would be located at the highest point where the coolant flows in the engine.
Originally it would have had DexCool.
If it is not losing coolant I would expect a plugged radiator.
sounds like a leaking head gasket have a pressure chek done on cylinders and cooling system
A pressurized coolant reservoir would have a thread on cap which acts as the " rad " cap
Originally it would have used Dex-Cool.
There is a sensor valve located inside the reservoir its may be bad