[Stocker]

At 43 oz. capacity, that tank is plenty good enough. 16# cap is fine (if it's for a closed system). No, you should not be pushing coolant out at only 210 degrees.

What typically happens is all coolant stays inside the cooling system until you turn the engine off. Then it will push some coolant into the overflow tank. As the system cools down, coolant will be drawn back into the radiator (if your cap is for a closed system).