[wizard]

No, don't run it with the cap loose. The coolant will heat up and expand and you'll probably have a mess under the hood as well as on the ground. Remove the temp sending unit which is located behind the stat housing and the air will escape there. Once you see coolant start to exit this opening, replace the sending unit and top it off. Then drive it and see what happens. Let it cool off and then recheck coolant level. WARNING, I suppose this goes without saying, but never remove a radiator cap while the engine is hot. Good Luck.