if it only drops a little then your okay, if it drops all the way to Cold again in a short space of time you got problems. most likely the thermostat playing up. this topic has been bought up many times and most of time its the thermostat. the temp gauge in the weather were getting, will drop slightly.bit less than half way-ish.. when your rolling in gear off throttle e.g down hill, the car will start to cool down. so if notice it drop slightly its okay. also you might be using your heaters, this also cools down the water temperatures, as your extracting the heat from the cooling system to keep yourself warm. remember this will only drop it slightly not all the way to cold again. hope that helps