Recall on Coolant caps

[rick3000]

The coolant level will change as it expands with the temperature, and as it is used by the car. Your coolant level will drop when you drive because the coolant is being run up the radiators, then when you park the coolant returns to the tank. (That's what the dealer told me anyway.)

Opening your tank right after driving is very dangerous. You need to let the coolant return to room temp before you open the coolant tank, and if nothing happens when the tank is at room temp. then there is probably nothing wrong.
Adding too much coolant can be bad because the tank will use the overflow above the passenger side rear wheel and leak the excess coolant out and possibly leak all of your coolant, which happened to me.