Surge tank
From the service manual:
During vehicle use, the coolant heats and expands. The coolant that is displaced by this expansion flows into the surge tank. As the coolant circulates, air is allowed to exit. Coolant without bubbles absorbs heat much better than coolant with bubbles.
Surge Tank
The surge tank is a plastic tank with a pressure cap mounted to it. The tank is mounted at a point higher than all other coolant passages. The surge tank provides an air space in the cooling system. The air space allows the coolant to expand and contract. The surge tank also provides a coolant fill point and a central air bleed location.
During vehicle use, the coolant heats and expands. The coolant that is displaced by this expansion flows into the surge tank. As the coolant circulates, air is allowed to exit. This is an advantage to the cooling system. Coolant without bubbles absorbs heat much better than coolant with bubbles

now you will notice C6 has 2 lines that connect to the surge tank. item 17 comes from top passenger corner of radiator, item 21 comes what is called stem vent or top most parts of the engine. both will let air get sent to the overflow if there is air bubbles or ust collant if no air. note item 10 comes from lower part of fill/surge/overlow tank and is sent back to the engine. there seems nothing to stop a constant flow from occuring.














