A coolant leak cost can vary greatly depending on what is leaking and from where. A coolant leak can be as simple as a loose clamp, or it can be a heater core that’s leaking. A leaking heater core can take as much as eight to ten hours to replace. At $80 an hour for labor, that’s anywhere from $720 to $800 in labor alone. If the leak is a hose that needs replacement, you can expect to pay for an hour’s worth of labor, plus the hose and replacement coolant. If the radiator is leaking, you can expect two hours of labor, plus replacement coolant.