OK I rarely drive my car now. A trip to school maybe once a week, a trip to the grocery store and thats about it. Under 100 miles a week.

That being said, since the summer I had a coolant loss problem. Went through about a gallon of mixed coolant in three months.

Took the car to a new shop that comes highly recommended by everyone (I have great faith in them). They said the leak was from some corrosion on some of the hose fittings. All cleaned and pressure tested and all was good. So I'm happy. But then this weekend, 1 week after getting the car back, the expansion tank is empty. I'm wondering if it was just the system filling up a bit better after being filled or what? I tossed in more coolant and hopefully it sticks around.

The question is: If they pressure tested the system, could it still leak coolant? And from where? Radiator Cap?