I found this on a different forum but thought it would be helpful to put on here. I think the car pictured is Grand Prix, but its a 3800 V6 so this is just a general how to.

The radiator drain plug/valve is located on the driver's side of the radiator towards the engine. To access it you will have to jack up the front driver's side of car, then remove the plastic splash guard and/or air deflector from underneath the car. Several bolts secure the plastic. Once that is removed all you need is a ratchet. Insert over plug and turn about 1/8" - 1/4" counterclockwise. Coolant will drain.

Note: The coolant may be hot so follow proper safety procedures, let engine cool down and when jacking car up be sure to use jackstands.

The pics below show the drain plug and hopefully should be self explanatory.

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