Sunday night on my way home from work (-5 degrees) my car overheated, stopped at gas station and let cool down for half hour and added premixed antifreeze (1/2 gallon) most of what was lost got puked out overflow jug. my question is do I have to change that thermostat or can I get lucky and just fill it back up and go?

First things first. Is it a bad thermostat or did you just jump in and start driving without letting it warm up first? You need to remember that the air over the radiator is a lot colder then the outside temp. It could be you just froze the coolant which my have been thinned out some.

Tstat would be a likely suspect. I would for sure open it up & check it out & go from there

I did let it warm for a short while , but not all the way. I'm going out now to look at it 30 degrees now.

I am betting that you froze the coolant up. Stats sticking is rare. Sure what blew out was liquid but the coolant crystalized and couldn't flow.

if its cold enough and the antifreeze is watered down some it will freeze up while driving. had it happen to me sometime ago stopped for a while till it thawed then drove allitle slower till it warmed up then it was fine, just added some more antifreeze. hope this helps

I've had thermostats stick open (90 Dakota) and closed (78 Magnum), so it does happen, they are not generally high quality pieces. But both of these happened in moderate temps. Your's seems suspicious given the cold temps. What did you find?