Driving to work yesterday in about 75°F weather, the thermostat rose to the 2nd highest red notch. The highest speed limit on this route is 35; I was able to pull over quickly and let the car cool down. <p>Anti-freeze bubbled out of the coolant reservoir, so I didn't think that could be causing the problem. Oil was fine. I've noticed recently that the fans have been making a lot more noise than usual, but this is the first full summer that I've had the car, so I didn't really have a baseline. It eventually cooled down enough that I could drive the remaining few miles to work, and the needle only rose a knotch or two the rest of the way.<p>On the way home from work, the thermostat reached the red zone again within only about 3 minutes of driving. I pulled over again, let the car cool down. oThis time the coolant reservoir looked like it could take some liquid. It took about a quart. The rest of the drive home went fine - the thermostat barely moved from the 3 o'clock (half-way) position.<p>I have no coolant leaks, only the noisy fans. Has anyone else experienced over-heating while only being down a quart of coolant? Could the extra coolant have solved the problem, or should I look into have fans replaced?