My van keeps overheating what is the problem? (1998 Chrysler Town & country)?

[Ann]

When i start the van up in the morning it takes about 5 to 10 mins before it overheats with or without the heat running. With its in neutral & the heat on, it takes 2 mins to cool down to where it should be. Water comes out the overflow tank, no where else, no steam, no water leaking anywhere. I can hear the air pockets when inside the van. I can't go over 45 without it overheating right away. What is wrong with my van? What can I do to fix it? I took the thermostat out when i replaced the heating hoses should i put it back or keep it out