How long can a heater core leak?

A heater core leak can last anywhere from a couple days to several years, depending on the severity of the leak and the type of vehicle. Usually a heater core leak will cause the vehicle's coolant level to drop, which can cause the engine to overheat. If the leak is severe enough, it can also cause the heater to stop working. In most cases, a heater core leak will require the replacement of the heater core, which can be a costly repair.