Hi. I'm losing coolant and thought it was the expansion tank. But after removing carpet and such, no leak. Car has never overheated, so I refilled and brought back up to operating temperature. I noticed a leak under car near center, maybe just forward of center. After removing shield, its coming from a drain. What is this drain for? Could it be heater core? How can you tell if it is heater core or heater valve? Sorry for all the questions, any help would be appreciated.