Temperature problem in Saturn

I have a 1997 Saturn sc2 standard 160,000 miles 1.9liter. Lately my car seems to have a temperature problem whe n it just sits in nuetral after about 9 minutes. I noticed the problem after getting in some severe traffic. I started to notice that my temp was slowling moving up and eventually got to the mid line. Also the car started to seem just a tad sluggish until I got out of the traffic and started to drive for a bit. Once I got to my destination I opened to hood to find that a small amount of radiator fluid had leaked out through the cap and there was a colored fluid stain that went down the radiator reservior to the ground. Couple days later I just turned on the car and left it in nuetral and it did it again and I decided to drive around my block and as I drove the temp went back down. Is my radiator having some kinda problem with the car sitting in nuetral or is there some sensor not working correctly?