Hi ,  I have Nissan maxima 2018, american specs at 106000KM currently. Recently I had to do bypass on the heather core since it started leaking and heating is really not needed where I live however I have noticed now when engine Is cooled overnight and I open radiator cap pressurised air with a bit of coolant goes out through reservoir overflow that causes me to need to add a bit of coolant in radiator.   I have changed thermostat, checked water pump, replaced as well radiator cap genuine one.  However issue is still there.  Thought could be gasket but I dont have any sign that could state that except that air by the way it lasts literally a second after I open radiator cap.  Dont have overheating, no white smoke, checked oil , no bubbles in coolant nothing at all to point me out in right direction.  Any ideas ?  Or think that is gasket ?   Thank you