Air in the cooling system. and creates air pressure? Thermostat may be missing. ? hoping for some help

The radiator on my car quickly loses water and the gauge on indstrment board goes up when I accelerate quickly or revolutions are loud as on the highway. when I run into the emergency lane to fill water or cool the engine and decreases the water cap is a huge pressure off the hood of even though almost no water is left. and in the coolant tank can sometimes also be empty. I myself think it is because there is air in the system? my mekanier have aired it a couple times where I can run undisturbed a long while. I have a thermostat I have been with and am not sure whether it can be the outstanding problem. Hopes high on something tackled. Greetings kenneth