Coolant Problem

My 97 Z is having some cooling issues. After driving my car for 30 min. or so and when it is nice and hot my low coolant light comes on. It has been doing this for the past week. After parking the car today I noticed that my over flow tank was overflowing (coolant was leaking out of the cap). When my car cools off my anti-freeze is filled to the neck in the radiator and where it should be in the overflow tank. Since I've had the car (for about a year) it has not overheated.

Why is my low coolant light coming on when it is filled with the correct amount and why is coolant overflowing out of my car?

have you replaced anything in the cooling system recently?

have you replaced anything in the cooling system recently?

No I haven't replaced anything. I plan on flushing the coolant this weekend. Would a bad thermostat be the source of my problems?

Maybe, if it's just sticking. Pressure from the now super heated coolant finally forces it open, and it then starts to boil the coolant in the remaining part of the cooling system, causing the overflow. I don't really think that's the problem, but it's a cheap place to start.