I usually replace the engine coolant every 30k miles or so. I know that by draining the radiator, only about 1/2 of the c total coolant comes out. Does my car have a radiator petcock, or did GM eliminate that some time ago? Do you have to pull off the lower radiator hose to drain the coolant? How much is needed to refill the system on the 3.9 liter V6 engine?