Some signs that your heater core is bad is engine overheating, or loss of engine coolant where no other leaks can be found.
Your heater may be putting out little or no heat at all, windows fogging up, coolant smell inside your vehicle or you see signs of coolant leaks on the floorboard that is coming from your dash.
Sometimes your heater core could just be clogged up and may only need to be flushed out but if the heater core is leaking it cannot be repaired and needs replaced.
Replacement costs for heater cores can range from $500.00 to $1,000.00 for parts and labor depending on make and model of car.
If you replace the heater core yourself it may only cost you $50.00 to $200.00 for parts and then the time it takes you to replace the heater core.