2001 Buick Century Custom

There are more things involved than just the coolant. The cheapest fix is a new thermostat. If the car is loosing coolant and it is not running out under the car, it could be a gasket and the coolant is going into the engine....check the oil dip stick for foam and or a high over fill reading. You could also have a plugged radiator.

first stop driving if fluid is in it when its cold check the radiator make sure its full there and overflow then turn ac on to see if fan turns on if it does it works if not its a fan issue then start it and watch to see if its leaking from a hose or anything that causes fluid to leave then wait a few minutes for it to heat up if its over half way the fan should kick on if it doesnt and its getting hot and smoking probably the thermostat if it does then it could be a head gasket or something if the coolant is brown and gross thats not good if it isnt thats good make sure to not drive hot or it will its possible to have some air in there if theres a bleeder screw you can release it if not jack up the front end and fill it with the cap off start it if it goes down fill it til it doesn't