Coolant has a fairly distinct smell. When the engine begins to warm up and you pop the hood, do you smell anything? The coolant system is pressurized and a small leak may simply vaporize, but you may be able to smell it. Based on what you're describing, if you're running the car, I wouldn't let it get much warmer than when the electric fan turns on. That's usually around the point where the thermostat opens up to allow coolant to be circulated to the radiator and cooled. Air going through the radiator indirectly cools the coolant and when the car isn't moving, the fan provides all of the air circulation.