Nice try green coolant? Ha!
The Chevy Cobalt like every other Chevy after a certain year uses Dexcool which is Orange. Dont use the green coolant because you will destroy your engine, and cooling system. Dexcool + Green Coolant acts like a acid.
Just drain the coolant out of the botom with the plug, make sure not to spill any on the ground, put a low power water hose into the radiator and let it run water through drain all water, then refill the radiator with the plug back in with Dexcool only.