Why my 1990 Chevy Astro Van LT AWD drains new battery completely dead

Yeah, I'd say you got some problems... might want to start by getting charging system tested, alternator and battery. A typical parasitic drain can't discharge a battery in mere hours, so you either got a motor running (fuel pump for instance) or a battery with a dead cell. Get those load tested. Thick white smoke is never a good sign, usually it means you're burning coolant, and can be a sign of a blown gasket. The "thump" under the floor can be caused by a worn torque converter lockup clutch, either catching or releasing when it shouldn't. If you're not a mechanic then maybe take this heap to one, or start planning on replacing the vehicle.

well i try not to pick sides, but this time I would say these only have problems get a car or van get rid of it