Wrote this for another forum but it mostly applies to a G6:
Have the car cooled down, remove the cap on the coolant reservoir. you will need to fill this up almost completely. let it sit for a few minutes, keep checking the level. it will probably go down a bit, and burp some air bubbles. Air will naturally rise to the highest point, which is why coolant tanks are higher than the coolant passages in the engine.
After you do this for about 10-15 minutes, start the car with the coolant cap off. Let it run for a few minutes, you will need to turn the HVAC control to full heat. Next, open the purge screw. You will get coolant coming out of it. After you let that flow for a minute, close it. Let the engine run for about 10 minutes, check the temp gauge periodically. You can now put the cap back on the reservoir after you check the coolant level with the engine running. Make sure it has plenty of coolant in it. You should have hot air blowing from the vents, & the temp gauge should read normal operating temp. Shut off the engine, let it cool for a few minutes, recheck the level.
Last edited by greenman; 10-25-2011 at 11:45 PM.