coolant draining back into resivoir or possible air pocket
Consider replacing your radiator cap . .
You are having a overheating problem. You failed to mention a description of the car. If it has an electric cooling fan then you need to be sure it is working.
Test or replace the sensor in the radiator side tank.
a bad radiator -automatic portion of radiator not cooling off transmission
The fan should turn off after the engine is shut off. If it stays on, the radiator fan relay has failed.
Smoke from the radiator would be do to a leak evaporating off of it. Find the leak repair or replace necessary parts.
Pressure could be building in the shut off system, and the extra comes back into the bottle. If you are loosing coolant over time then air in the bottle probably means that you have a blown head gasket.
u turning it off
Turn it off. Let it cool off and then see if it has a coolant leak or radiator leak. Don't open the radiator when hot because the hot water will spray out.
Replace the thermo sensor...
First, start when the engine is cool. The radiator does not have a drain plug. What you do is loosen one of the radiator hoses. Take a garden hose and start putting the water directly into the radiator and turn the van on. Let the water flow throughout the radiator and the motor. Turn on your heater to get the heater components opened and flushed out also. Run the water throughout the radiator for a few minutes. Turn the van off. Turn off the heater. Repeat this step until the water runs clear out of the hose hole that was taken off in the beginning. Next, after you have flushed it twice, connect the hose that you took off. Turn the van on and start adding radiator fluid into the radiator. Don't overfill the radiator. While the van is running, the radiator fluid is being cycled throughout the engine. Watch the level of the radiator fluid and if it goes down, add more fluid. You will repeat this step several times because of all the radiator fluid cycling throughout the motor. You might have a little bit of fluid left, put this into the radiator fluid over flow container on the right side of the motor. Once you have added all of the radiator fluid, keep the van running for about 10 minutes and during this time, turn the heater on. If you find out that the heater is blowing cold air, after the 10 minutes, turn the van off, let it stand for about 5 minutes and turn it back on. The heater should be working now. The van just has to reset everything.
The radiator fan on a 1998 Plymouth Voyager won't turn off if the engine is overheating or the temperature sensor is defective. The fan is designed to only work once the temperature has pass a certain threshold.