It's defective.
Maybe it's not the radiator. Maybe it is one of the radiator hoses that is leaking. Or possibly the radiator cap or a level sensor.
Sometomes it is hard to get all of the oil out of the cooling system. However the place that replaced the engine should flush the cooling system until it is clean. Also if your car has an engine oil cooler , it could be the cooler in the radiator and not have been the engine in the first place.
If a lower radiator hose was replaced on a 1999 Dodge Grand Caravan, but it is still leaking fluid, it could be that there is a hole in the radiator. It could also mean that there is damage to the overflow reservoir or its hoses.
A car with a leaking radiator can be driven, but when the coolant leaks out, the engine will overheat and when the engine gets hot enough, it will seize-up, the car will stop, and the engine will have suffered severe damage.
Your radiator is probably leaking transmission fluid into your coolant. Trans cooler is built into the radiator. Replace the radiator.
Either the water pump impeller is loose on it's shaft, or you have a leaking head gasket.
Possible cracked block or a blown head gaskets.
tighten up the hose you think it is and see if it still leaks if it does still leak then its either a cracked hose or crack in your radiator
If it's leaking at the radiator, make sure you haven't accidentally bent the fitting. Sometimes a brass fitting can be accidentally bent and you'll never get it to seal until it's round and cleaned up. If it's leaking at the block or water pump, make sure it's clean and there are no large corrosion pits. If everything looks good at those locations, check for leaks elsewhere. The radiator could be leaking where the hose connects. The water pump could be leaking and it only LOOKS like it's leaking at the hose.
Blown head gasket?
the radiator was replaced and the fluids are still evaporating or leaking out somehow. what other options could be wrong with the car overheating?
I would check the radiator coolant bottle for cracks and inspect any hoses to bottle.