No, they don't. There is nowhere for them to go. It is what in engineering is called a CLOSED system. That is why the air needs to be VENTED OUT, as completely as possible. Without getting into the scientific details, tiny air bubbles can and will be pushed through by a pump if these tiny bubbles are a small percentage of the liquid volume. Water pumps cannot pump air. Period. That's why your engine overheats if there is an air bubble in the FRESHWATER coolant side. The freshwater carries the engine heat to the HX where the seawater cools it and returns it to the freshwater loop via the freshwater (coolant) pump. If that pump hits a block of air, movement of even the liquid stops.Really small ones probably work themselves out also I am rough guessing....
Take a look at the freshwater coolant loop on your engine to understand, if you don't already. Here's a good example:
- Flow directions in engine cooling hoses (both early and B-series engines) --KWKloeber 2/2/2019