My 2003 Dodge Ram Van is over heating within the span of 15 to 20 minutes. I can put the van in neutral and rev the engine and that draws the heat in the van and seems to cool the engine. I does not work all the time. I checed the coolant tank and it was completely empty but show no signs of leaking. I have since filled up the coolant and that did not seem to work. Should I put some coolant directly into the radiator to help move the coolant? What could be going on?

Check the oil level and see if there's coolant in the oil. You may have a warped head and a leaking head gasket ($2,500+). This should be checked out right away. You need to determine where the coolant is going.

This link may help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-46563-3.html#post235973

You seldom have to see water in the oil gasket leak pressure into the water creating steam pockets that expand rapidly blowing out the coolent that's all that's nessesary

The coolant can also disappear through the exhaust : look closely at the exhaust and see if it's coming out there.I onced had a car with a broken head-gasket and coolant came out through the exhaust.If it's not leaking out visually it has to be going some where.

Yes I would put it directly into the radiator and make sure the water pump is working .Hold the radiator top hose and rev. the engine to feel the pressure from the pump or look into the radiator and see if the water appears to be moving.Has the thermostat been changed recently and is the serpentine belt in good condition?