water will not circulate between the engine and resivor unitl the thermostat opens at least on my car. Not sure if the 4 cylinder cooling system is plumed differntly than a 6 cyl. or not.

When the coolant/water mixture is agitated it makes lots of tiny bubbles.

I feel sorry for the people who don't drink. When they wake up in the morning, thats the best they're going to feel all day - former President Lyndon B. Johnson