How can you tell if heater core needs replacing?

Anti-freeze smell inside vehicle when you turn on the heat. Greasy windshield from the anti-freeze leaking from the heater core while the heat is running. Also check the passenger side of the vehicle carpet under the carpet and check the heater core hoses under the hood of your vehicle for anti-freeze leaking at the fire wall where the heater core hoses go. That about covers it. If all checks out do a pressure test on your anti-freeze circuit and this will definitely bust the culprit of the leak. Last of all, if you have no leak and your heat is not working and the heater core is in circuit with the anti-freeze with no leaks, replace the heater core. C.S