What causes a 1992 Dodge Caravan 3.3 ltr engine to blow steam out of the exhaust pipe?

Had the same problem with my 94 Grand Caravan 3.3L. You have a blown head gasket.
Cost me 4 grand to have the motor rebuilt. Good Luck and Remember.
Change Your Mind, Not Your Oil.
Use the First In Synthetic Motor Oil's.
See My Bio For more information. I don't want to come off as flippant, but the main two reasons I know for getting steam out the tailpipe are a blown head gasket or a cracked block. I do not know much about the 3.3l engine, but I would suspect the head gasket over the block UNLESS you know of some other "bad" that has happened (freezing solid, throwing a piston rod, etc.). If you take off the radiator cap and see oil, the head gasket seems highly likely to me. Unusual bits of metal on the oil drain plug would lead me to fear for the block, maybe. Sorry not to be more definite, but maybe some one with experience with this motor will be disgusted by my feeble attempt and offer some true insight?