Hi from justanswer!
The most likely cause of this is a sticking thermostat, which is located on top of the engine just below one end of the upper radiator hose.
Before you replace the thermostat, be sure that flow around the cooling systrem is normal. With the van warmed up (not overheating) turn the heater on high speed and hot. If you get plenty of hot air to the floor, then coolant is circulating properly through the engine and heater core. Until the thermostat opens, however, coolant is not sent to the radiator. When replacing the thermostat, be sure to flush the radiator itself and make sure it isn't blocked by any rust, gum or debris
If you do not have hot air coming into the vehicle through the heater, then there is a more serious problem. Either coolant is not circulating, or there is a bubble forming in the system when the engine is running. In either case, engine work is necessary for either a defective coolant pump, severe blockage in the system or a leaking head gasket.
tenbear, I was editing the post while you were reading - sorry.
There is a chance that coolant is leaking from the connection between the raditor and the overflow. Is the radiator cap on the opposite side?
I'm going to see if chat is working so stay tuned.
Chat not working. Hm.
Cooling systems can leak only under pressure. Your van should hold up to 16 psi but a pressure leak will let coolant out and air in after you drive it. If your overflow bottle stays full, it's because air is inside and pushing coolant back out of the bottle instead of sucking coolant back in.
You might have to home in on the leak and fix that before you can figure out any overheating issues. A coolant pressure test can make the system leak for you without you having to warm it up.
16psi is the rating of the radiator cap, so if antifreeze is coming out anywhere but the cap your level will drop until the van overheats. Also, if antifreeze leaks onto the radiator support, it can come out on the ground somewhere far away from the actual leak. A good look under the van will turn up anything obvois, but use a pressure tester instead of running the van. It's easier to inspect when it's not too hot to touch.