If your heater core was leaking, you'd find coolant inside the car. So it's probably not it.
Check your water pump, thermostat housing, freeze plugs, radiator, double checks radiator hoses and heater core hoses. I suggest you check with engine on; it makes it easier to detect the leak since the cooling system is under pressure.
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Saturday, February 9th, 2019 AT 3:58 PM