How do you know if heater core is going out T

When the antifreeze runs out -- where is it going? Have you verified a leak? If it's leaking, and you don't know where to, you need to have your cooling system pressure tested to find where the coolant is coming out. It may or may not be related to a heater core leak -- no need to jump to that conclusion without confirming it via testing. www.repairpal.com/repair-shops