Yes it closed loop. Every car since the mid 50's works on the pressurized sealed system. Unless you have had a cooling system part replaced, or a service already, there would be no air in your system. The only way you would have air in your cooling system is if the system has been drained and improperly filled/bled. If that were the case you should have seen sporadic heat inside or even overheating.
Tks. Was just getting rid of paperwork from the ‘17 and found last service call where I had it towed in bc the reservoir had drained while sitting at the airport for a week in April. Left it for a week and started her up and got the check coolant level light. Tank was bone dry. Added a little water then drove home. They checked the system, found no issue and said an air bubble caused the problem. Didn’t understand how that could happen. Finding the paperwork made me think of it. Tks.