my 95 grand am is going through antifreeze like crazy but no leak what could it be

first check oil if white milkey looking blown head gasket.if clean oil, you could have a head gasket blown on exhaust side see if tou see excess steam comming ouy of tailpipe if not check all hoses,may want to change thermostat refill with water see what happends also check water pump.

Yes, do all of those things, have a pressure test done on the cooling system to see if the leaking is internal. It could be an intake manifold gasket as well, I believe the '90s Grand Ams were known for head/intake manifold gasket leaks. Also you might want to check for pinhole leaks at the bottom of the radiator -- had a car once that emptied the coolant reserve EVERY MORNING, later found out a small pinhole leak was allowing it to drip out the bottom of the radiator, pool on a frame rail, and of course blow off while driving so you never saw a puddle.