So being new to car maintenance and looking around under the hood I went to look at my coolant levels today instead of opening the reservoir cap I ended up opening the Radiator Cap instead, my question is does opening this cap cause air to leak in? Thank you

 

Was the engine hot or cold when you opened up the radiator cap? If it was cold, opening it up probably did nothing. The coolant was probably at the top of the neck of the radiator, and there was nowhere for air to get inside the radiator anyway. Our cooling systems are closed systems attached to an overflow tank. As the coolant heats up and expands and exceeds the max pressure of the radiator cap, the excess fluid goes into the overflow tank. When the system cools down, that excess fluid is drawn back into the radiator until it is full. The overflow tank is vented, so if there ever is any steam from a hot engine, it expels through the vent.

 

My engine was cool and hadnt ran the car all day, I didnt bother removing the cap from the coolant reservoir at this point but i definitely removed the Radiator Cap

 

^^56chevydan is correct. In the future, if you want to check your coolant levels, check the reservoir. Leave the radiator and radiator cap alone (as a general rule). The reservoir is marked with Upper and Lower coolant level limits.