The shop I've used for years has had some turnover and wonder about the experience or integrity of new guys hired...if they can find them. It is just speculation on my part about the fill trying to guess what happened. Some concern now of any ills that might crop when a motor gets overheated...Any mechanic worth their weight should be able to get all the air out of the system after a thermostat change. But, then again, some techs are so full of hot air that they weigh a lot less than others.