My temperature gauge on my 2000 zx2 always sits a little above a quarter of the way up from the cool line, well last night I had ran a trip to the store to get some food and I noticed that the temperature gauge was sitting a little above half way, which it has never done the entire 7 months I have had it. I parked it back on base and left it alone. When I went to get into the car today I checked the coolant and the overflow was empty but the radiator was full. I started the car and the temp gauge was already sitting where it was suppose to be when the car was running normally and I did a lap to get back out and see the cap was on. There was about a five to seven inch round puddle of antifreeze on the ground, but the cap wasn't on all the way. I fixed the cap and went on my merry way. I could see my temperature gauge bouncing between below half way and above it. Everytime there was stress on the engine it would go up, but then it would go down sometimes when I shifted. I stopped and checked for a puddle and there was a little two inch puddle under the car. I got in and the temp gauge was reading higher than before. I go to my next stop and no puddle but the car is now not idling around 900 rpm like it use to and was barely idling around 200 or 300 rpm and sometimes bouncing up to 900. The temp gauge was doing the same thing as it was when I first got on the road, then when I hit traffic on base it just got hotter and hotter and hotter until i could park it. I was just wondering if anyone had any advice to help point me in the right direction of something like the water pump, thermostat, or just a bad radiator cap. Any help would be appreciated.