I have a 2006 cobalt and need to add coolant, what kind is reccommended? I do no have an owners manuel

The factory coolant is Dex Cool. It is a yellow/orange color as opposed to the other type which is green. Do not mix the two. Apparently that is very bad. Find out for sure which you have so you don't add the wrong one.

Check to make sure the drop in coolant is just normal evaporation, even though it is a closed and sealed system. Check the water pump for any wetness or signs of leakage. The hose connections should also be checked. Is there any colored water under the car after being parked for a while? A good pressure check will reveal any possible leaks. Follow the advice from munron on what to add. If you keep adding more and more antifreeze, you have a problem. You also may be putting in too much anti freeze so get the system checked.

dex cool just get 7 letters of that stuff your set