Heater cores are typically replaced whenever something goes wrong with them, such as a leak, according to AutoEducation. There is no definitive time to replace a heater core, as they are not a part of typical scheduled maintenance.
One recommended way to maintain the functionality of a heater core over time is to change coolant every 25,000 to 40,000 miles, YourMechanic explains. The heater core is similar to a small radiator, and making sure clean coolant is running through it helps reduce the chance of blockage. Sometimes a heater core leaks or breaks, which is generally signified by steam emanating from the automobile's heat vents and leaking coolant under the dashboard.