2005 Chevy Cobalt I think its the head gasket but I dont kn

2005 Chevy Cobalt 54,000 miles

like my car was wrecked and it still drives but there is something wrong with it we replaced the radiator and we got it put on a machine that said that the sparkplugs needed changed we havent got to do that yet but their was another code on it that they couldn't read and we dont know what that is. But the problem is like the water, we keep having to put more and more in it. So everytime we go to put water in it, it will cut out when we go to drive it and while we are driing it it gets like heated up it guess and it wont start when we go to start it ulp again it wont and it takes forever for it to cool down and I dont know whats wrong because I have smoke that comes out the back of my car too. Like my car drives just fine with no water I know that sounds crazy but it does and we put the water in and it messes up. But we can drive it practically any where? So what do you think it wrong with it? And what estimate do you think it will take for it to get fixed? We have and offer of 1900 to get it fixed is that good? Please help me. Lol