White smoke from exhaust pipe

I have a E-250 conversion van, 62, 00 miles, 2001,
After returning from a 2,000 mile trip and the van sitting for 3 days I started it up and noted a lot of while smoke from the tail pipe and condensation.
Your site noted that white smoke maybe condensation, however noted to watch the level of the antifreeze, why? What are some of the other possible causes for the white smoke?