Overheating 2000 dodge Neon changed the thermostat what else could be the problem?

I already had the thermostat changed and now all I need is a new coolant reservoir tank, how long can I go without a new coolant reservoir tank, the one that's is in the car now has a very small hole in it, I was told that I have to get one soon and keep checking the fluid level and I should be fine. I also want to know when the coolant reservoir tank is replaced should there be anything else that I should worry about? ThanksOverheating 2000 dodge Neon changed the thermostat what else could be the problem?you,ll have to get it replaced pretty soon because when it heats up the coolant wont have a storage tank an this will make it run low on coolant real fast,you might make it a few days or so but keep a close watch on the coolant level on this you really don't want to do is run that car hot,after you replace the tank on it be sure the coolant mixture is right on it and you should be alright with it,good luck with it.Overheating 2000 dodge Neon changed the thermostat what else could be the problem?i do know you can go to your local autozone or advance auto parts or orillys they usually have replacement ones if they dont have it then they can order itOverheating 2000 dodge Neon changed the thermostat what else could be the problem?watch out you dont blow the head gasket they are bad for that i just done one