Temp gauge went up and down and finally into the red. I checked and found no leaks, fan was working, neither the a/c or heat was on, coolant level was good, radiator is about 2 years old. I'm hoping it's as simple as a thermostat problem. If so, where is it and is it easy to replace? I'm not a mechanic but not afraid to try if it's "reasonably" easy, meaning I don't have to put the car up in the air and it's possible to just have to crawl underneath.