Download NOTE: Vehicles may be equipped with an aluminum or a copper brass heater core. Use replacement cores made of copper brass. Always identify the type of core being replaced because there is a difference in the heater core to heater case seals. Having the correct seal is essential to provide satisfactory heater system performance. Identification can be made by looking at one of the core tubes after a hose has been removed. An aluminum core will have a gray colored tube. A copper brass core will have a brass colored tube. If the core is copper brass, the seal removed with the old core can be used with the new copper brass replacement core, providing it is not damaged during removal. If the core is aluminum, a new seal for the copper brass replacement core will be required.